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• Joins in LINQ to SQL

  - by rajbk

  The following post shows how to write different types of joins in LINQ to SQL. I am using the Northwind database and LINQ to SQL for these examples. NorthwindDataContext dataContext = new NorthwindDataContext(); Inner Join var q1 = from c in dataContext.Customers join o in dataContext.Orders on c.CustomerID equals o.CustomerID select new { c.CustomerID, c.ContactName, o.OrderID, o.OrderDate }; SELECT [t0].[CustomerID], [t0].[ContactName], [t1].[OrderID], [t1].[OrderDate]FROM [dbo].[Customers] AS [t0]INNER JOIN [dbo].[Orders] AS [t1] ON [t0].[CustomerID] = [t1].[CustomerID] Left Join var q2 = from c in dataContext.Customers join o in dataContext.Orders on c.CustomerID equals o.CustomerID into g from a in g.DefaultIfEmpty() select new { c.CustomerID, c.ContactName, a.OrderID, a.OrderDate }; SELECT [t0].[CustomerID], [t0].[ContactName], [t1].[OrderID] AS [OrderID], [t1].[OrderDate] AS [OrderDate]FROM [dbo].[Customers] AS [t0]LEFT OUTER JOIN [dbo].[Orders] AS [t1] ON [t0].[CustomerID] = [t1].[CustomerID] Inner Join on multiple //We mark our anonymous type properties as a and b otherwise//we get the compiler error "Type inferencce failed in the call to 'Join’var q3 = from c in dataContext.Customers join o in dataContext.Orders on new { a = c.CustomerID, b = c.Country } equals new { a = o.CustomerID, b = "USA" } select new { c.CustomerID, c.ContactName, o.OrderID, o.OrderDate }; SELECT [t0].[CustomerID], [t0].[ContactName], [t1].[OrderID], [t1].[OrderDate]FROM [dbo].[Customers] AS [t0]INNER JOIN [dbo].[Orders] AS [t1] ON ([t0].[CustomerID] = [t1].[CustomerID]) AND ([t0].[Country] = @p0) Inner Join on multiple with ‘OR’ clause var q4 = from c in dataContext.Customers from o in dataContext.Orders.Where(a => a.CustomerID == c.CustomerID || c.Country == "USA") select new { c.CustomerID, c.ContactName, o.OrderID, o.OrderDate }; SELECT [t0].[CustomerID], [t0].[ContactName], [t1].[OrderID], [t1].[OrderDate]FROM [dbo].[Customers] AS [t0], [dbo].[Orders] AS [t1]WHERE ([t1].[CustomerID] = [t0].[CustomerID]) OR ([t0].[Country] = @p0) Left Join on multiple with ‘OR’ clause var q5 = from c in dataContext.Customers from o in dataContext.Orders.Where(a => a.CustomerID == c.CustomerID || c.Country == "USA").DefaultIfEmpty() select new { c.CustomerID, c.ContactName, o.OrderID, o.OrderDate }; SELECT [t0].[CustomerID], [t0].[ContactName], [t1].[OrderID] AS [OrderID], [t1].[OrderDate] AS [OrderDate]FROM [dbo].[Customers] AS [t0]LEFT OUTER JOIN [dbo].[Orders] AS [t1] ON ([t1].[CustomerID] = [t0].[CustomerID]) OR ([t0].[Country] = @p0)

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• Hello Operator, My Switch Is Bored

  - by Paul White

  This is a post for T-SQL Tuesday #43 hosted by my good friend Rob Farley. The topic this month is Plan Operators. I haven’t taken part in T-SQL Tuesday before, but I do like to write about execution plans, so this seemed like a good time to start. This post is in two parts. The first part is primarily an excuse to use a pretty bad play on words in the title of this blog post (if you’re too young to know what a telephone operator or a switchboard is, I hate you). The second part of the post looks at an invisible query plan operator (so to speak). 1. My Switch Is Bored Allow me to present the rare and interesting execution plan operator, Switch: Books Online has this to say about Switch: Following that description, I had a go at producing a Fast Forward Cursor plan that used the TOP operator, but had no luck. That may be due to my lack of skill with cursors, I’m not too sure. The only application of Switch in SQL Server 2012 that I am familiar with requires a local partitioned view: CREATE TABLE dbo.T1 (c1 int NOT NULL CHECK (c1 BETWEEN 00 AND 24)); CREATE TABLE dbo.T2 (c1 int NOT NULL CHECK (c1 BETWEEN 25 AND 49)); CREATE TABLE dbo.T3 (c1 int NOT NULL CHECK (c1 BETWEEN 50 AND 74)); CREATE TABLE dbo.T4 (c1 int NOT NULL CHECK (c1 BETWEEN 75 AND 99)); GO CREATE VIEW V1 AS SELECT c1 FROM dbo.T1 UNION ALL SELECT c1 FROM dbo.T2 UNION ALL SELECT c1 FROM dbo.T3 UNION ALL SELECT c1 FROM dbo.T4; Not only that, but it needs an updatable local partitioned view. We’ll need some primary keys to meet that requirement: ALTER TABLE dbo.T1 ADD CONSTRAINT PK_T1 PRIMARY KEY (c1);   ALTER TABLE dbo.T2 ADD CONSTRAINT PK_T2 PRIMARY KEY (c1);   ALTER TABLE dbo.T3 ADD CONSTRAINT PK_T3 PRIMARY KEY (c1);   ALTER TABLE dbo.T4 ADD CONSTRAINT PK_T4 PRIMARY KEY (c1); We also need an INSERT statement that references the view. Even more specifically, to see a Switch operator, we need to perform a single-row insert (multi-row inserts use a different plan shape): INSERT dbo.V1 (c1) VALUES (1); And now…the execution plan: The Constant Scan manufactures a single row with no columns. The Compute Scalar works out which partition of the view the new value should go in. The Assert checks that the computed partition number is not null (if it is, an error is returned). The Nested Loops Join executes exactly once, with the partition id as an outer reference (correlated parameter). The Switch operator checks the value of the parameter and executes the corresponding input only. If the partition id is 0, the uppermost Clustered Index Insert is executed, adding a row to table T1. If the partition id is 1, the next lower Clustered Index Insert is executed, adding a row to table T2…and so on. In case you were wondering, here’s a query and execution plan for a multi-row insert to the view: INSERT dbo.V1 (c1) VALUES (1), (2); Yuck! An Eager Table Spool and four Filters! I prefer the Switch plan. My guess is that almost all the old strategies that used a Switch operator have been replaced over time, using things like a regular Concatenation Union All combined with Start-Up Filters on its inputs. Other new (relative to the Switch operator) features like table partitioning have specific execution plan support that doesn’t need the Switch operator either. This feels like a bit of a shame, but perhaps it is just nostalgia on my part, it’s hard to know. Please do let me know if you encounter a query that can still use the Switch operator in 2012 – it must be very bored if this is the only possible modern usage! 2. Invisible Plan Operators The second part of this post uses an example based on a question Dave Ballantyne asked using the SQL Sentry Plan Explorer plan upload facility. If you haven’t tried that yet, make sure you’re on the latest version of the (free) Plan Explorer software, and then click the Post to SQLPerformance.com button. That will create a site question with the query plan attached (which can be anonymized if the plan contains sensitive information). Aaron Bertrand and I keep a close eye on questions there, so if you have ever wanted to ask a query plan question of either of us, that’s a good way to do it. The problem The issue I want to talk about revolves around a query issued against a calendar table. The script below creates a simplified version and adds 100 years of per-day information to it: USE tempdb; GO CREATE TABLE dbo.Calendar ( dt date NOT NULL, isWeekday bit NOT NULL, theYear smallint NOT NULL,   CONSTRAINT PK__dbo_Calendar_dt PRIMARY KEY CLUSTERED (dt) ); GO -- Monday is the first day of the week for me SET DATEFIRST 1;   -- Add 100 years of data INSERT dbo.Calendar WITH (TABLOCKX) (dt, isWeekday, theYear) SELECT CA.dt, isWeekday = CASE WHEN DATEPART(WEEKDAY, CA.dt) IN (6, 7) THEN 0 ELSE 1 END, theYear = YEAR(CA.dt) FROM Sandpit.dbo.Numbers AS N CROSS APPLY ( VALUES (DATEADD(DAY, N.n - 1, CONVERT(date, '01 Jan 2000', 113))) ) AS CA (dt) WHERE N.n BETWEEN 1 AND 36525; The following query counts the number of weekend days in 2013: SELECT Days = COUNT_BIG(*) FROM dbo.Calendar AS C WHERE theYear = 2013 AND isWeekday = 0; It returns the correct result (104) using the following execution plan: The query optimizer has managed to estimate the number of rows returned from the table exactly, based purely on the default statistics created separately on the two columns referenced in the query’s WHERE clause. (Well, almost exactly, the unrounded estimate is 104.289 rows.) There is already an invisible operator in this query plan – a Filter operator used to apply the WHERE clause predicates. We can see it by re-running the query with the enormously useful (but undocumented) trace flag 9130 enabled: Now we can see the full picture. The whole table is scanned, returning all 36,525 rows, before the Filter narrows that down to just the 104 we want. Without the trace flag, the Filter is incorporated in the Clustered Index Scan as a residual predicate. It is a little bit more efficient than using a separate operator, but residual predicates are still something you will want to avoid where possible. The estimates are still spot on though: Anyway, looking to improve the performance of this query, Dave added the following filtered index to the Calendar table: CREATE NONCLUSTERED INDEX Weekends ON dbo.Calendar(theYear) WHERE isWeekday = 0; The original query now produces a much more efficient plan: Unfortunately, the estimated number of rows produced by the seek is now wrong (365 instead of 104): What’s going on? The estimate was spot on before we added the index! Explanation You might want to grab a coffee for this bit. Using another trace flag or two (8606 and 8612) we can see that the cardinality estimates were exactly right initially: The highlighted information shows the initial cardinality estimates for the base table (36,525 rows), the result of applying the two relational selects in our WHERE clause (104 rows), and after performing the COUNT_BIG(*) group by aggregate (1 row). All of these are correct, but that was before cost-based optimization got involved :) Cost-based optimization When cost-based optimization starts up, the logical tree above is copied into a structure (the ‘memo’) that has one group per logical operation (roughly speaking). The logical read of the base table (LogOp_Get) ends up in group 7; the two predicates (LogOp_Select) end up in group 8 (with the details of the selections in subgroups 0-6). These two groups still have the correct cardinalities as trace flag 8608 output (initial memo contents) shows: During cost-based optimization, a rule called SelToIdxStrategy runs on group 8. It’s job is to match logical selections to indexable expressions (SARGs). It successfully matches the selections (theYear = 2013, is Weekday = 0) to the filtered index, and writes a new alternative into the memo structure. The new alternative is entered into group 8 as option 1 (option 0 was the original LogOp_Select): The new alternative is to do nothing (PhyOp_NOP = no operation), but to instead follow the new logical instructions listed below the NOP. The LogOp_GetIdx (full read of an index) goes into group 21, and the LogOp_SelectIdx (selection on an index) is placed in group 22, operating on the result of group 21. The definition of the comparison ‘the Year = 2013’ (ScaOp_Comp downwards) was already present in the memo starting at group 2, so no new memo groups are created for that. New Cardinality Estimates The new memo groups require two new cardinality estimates to be derived. First, LogOp_Idx (full read of the index) gets a predicted cardinality of 10,436. This number comes from the filtered index statistics: DBCC SHOW_STATISTICS (Calendar, Weekends) WITH STAT_HEADER; The second new cardinality derivation is for the LogOp_SelectIdx applying the predicate (theYear = 2013). To get a number for this, the cardinality estimator uses statistics for the column ‘theYear’, producing an estimate of 365 rows (there are 365 days in 2013!): DBCC SHOW_STATISTICS (Calendar, theYear) WITH HISTOGRAM; This is where the mistake happens. Cardinality estimation should have used the filtered index statistics here, to get an estimate of 104 rows: DBCC SHOW_STATISTICS (Calendar, Weekends) WITH HISTOGRAM; Unfortunately, the logic has lost sight of the link between the read of the filtered index (LogOp_GetIdx) in group 22, and the selection on that index (LogOp_SelectIdx) that it is deriving a cardinality estimate for, in group 21. The correct cardinality estimate (104 rows) is still present in the memo, attached to group 8, but that group now has a PhyOp_NOP implementation. Skipping over the rest of cost-based optimization (in a belated attempt at brevity) we can see the optimizer’s final output using trace flag 8607: This output shows the (incorrect, but understandable) 365 row estimate for the index range operation, and the correct 104 estimate still attached to its PhyOp_NOP. This tree still has to go through a few post-optimizer rewrites and ‘copy out’ from the memo structure into a tree suitable for the execution engine. One step in this process removes PhyOp_NOP, discarding its 104-row cardinality estimate as it does so. To finish this section on a more positive note, consider what happens if we add an OVER clause to the query aggregate. This isn’t intended to be a ‘fix’ of any sort, I just want to show you that the 104 estimate can survive and be used if later cardinality estimation needs it: SELECT Days = COUNT_BIG(*) OVER () FROM dbo.Calendar AS C WHERE theYear = 2013 AND isWeekday = 0; The estimated execution plan is: Note the 365 estimate at the Index Seek, but the 104 lives again at the Segment! We can imagine the lost predicate ‘isWeekday = 0’ as sitting between the seek and the segment in an invisible Filter operator that drops the estimate from 365 to 104. Even though the NOP group is removed after optimization (so we don’t see it in the execution plan) bear in mind that all cost-based choices were made with the 104-row memo group present, so although things look a bit odd, it shouldn’t affect the optimizer’s plan selection. I should also mention that we can work around the estimation issue by including the index’s filtering columns in the index key: CREATE NONCLUSTERED INDEX Weekends ON dbo.Calendar(theYear, isWeekday) WHERE isWeekday = 0 WITH (DROP_EXISTING = ON); There are some downsides to doing this, including that changes to the isWeekday column may now require Halloween Protection, but that is unlikely to be a big problem for a static calendar table ;)  With the updated index in place, the original query produces an execution plan with the correct cardinality estimation showing at the Index Seek: That’s all for today, remember to let me know about any Switch plans you come across on a modern instance of SQL Server! Finally, here are some other posts of mine that cover other plan operators: Segment and Sequence Project Common Subexpression Spools Why Plan Operators Run Backwards Row Goals and the Top Operator Hash Match Flow Distinct Top N Sort Index Spools and Page Splits Singleton and Range Seeks Bitmaps Hash Join Performance Compute Scalar © 2013 Paul White – All Rights Reserved Twitter: @SQL_Kiwi

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• SQL SERVER – Weekly Series – Memory Lane – #038

  - by Pinal Dave

  Here is the list of selected articles of SQLAuthority.com across all these years. Instead of just listing all the articles I have selected a few of my most favorite articles and have listed them here with additional notes below it. Let me know which one of the following is your favorite article from memory lane. 2007 CASE Statement in ORDER BY Clause – ORDER BY using Variable This article is as per request from the Application Development Team Leader of my company. His team encountered code where the application was preparing string for ORDER BY clause of the SELECT statement. Application was passing this string as variable to Stored Procedure (SP) and SP was using EXEC to execute the SQL string. This is not good for performance as Stored Procedure has to recompile every time due to EXEC. sp_executesql can do the same task but still not the best performance. SSMS – View/Send Query Results to Text/Grid/Files Results to Text – CTRL + T Results to Grid – CTRL + D Results to File – CTRL + SHIFT + F 2008 Introduction to SPARSE Columns Part 2 I wrote about Introduction to SPARSE Columns Part 1. Let us understand the concept of the SPARSE column in more detail. I suggest you read the first part before continuing reading this article. All SPARSE columns are stored as one XML column in the database. Let us see some of the advantage and disadvantage of SPARSE column. Deferred Name Resolution How come when table name is incorrect SP can be created successfully but when an incorrect column is used SP cannot be created? 2009 Backup Timeline and Understanding of Database Restore Process in Full Recovery Model In general, databases backup in full recovery mode is taken in three different kinds of database files. Full Database Backup Differential Database Backup Log Backup Restore Sequence and Understanding NORECOVERY and RECOVERY While doing RESTORE Operation if you restoring database files, always use NORECOVER option as that will keep the database in a state where more backup file are restored. This will also keep database offline also to prevent any changes, which can create itegrity issues. Once all backup file is restored run RESTORE command with a RECOVERY option to get database online and operational. Four Different Ways to Find Recovery Model for Database Perhaps, the best thing about technical domain is that most of the things can be executed in more than one ways. It is always useful to know about the various methods of performing a single task. Two Methods to Retrieve List of Primary Keys and Foreign Keys of Database When Information Schema is used, we will not be able to discern between primary key and foreign key; we will have both the keys together. In the case of sys schema, we can query the data in our preferred way and can join this table to another table, which can retrieve additional data from the same. Get Last Running Query Based on SPID PID is returns sessions ID of the current user process. The acronym SPID comes from the name of its earlier version, Server Process ID. 2010 SELECT * FROM dual – Dual Equivalent Dual is a table that is created by Oracle together with data dictionary. It consists of exactly one column named “dummy”, and one record. The value of that record is X. You can check the content of the DUAL table using the following syntax. SELECT * FROM dual Identifying Statistics Used by Query Someone asked this question in my training class of query optimization and performance tuning.  “Can I know which statistics were used by my query?” 2011 SQL SERVER – Interview Questions and Answers – Frequently Asked Questions – Day 14 of 31 What are the basic functions for master, msdb, model, tempdb and resource databases? What is the Maximum Number of Index per Table? Explain Few of the New Features of SQL Server 2008 Management Studio Explain IntelliSense for Query Editing Explain MultiServer Query Explain Query Editor Regions Explain Object Explorer Enhancements Explain Activity Monitors SQL SERVER – Interview Questions and Answers – Frequently Asked Questions – Day 15 of 31 What is Service Broker? Where are SQL server Usernames and Passwords Stored in the SQL server? What is Policy Management? What is Database Mirroring? What are Sparse Columns? What does TOP Operator Do? What is CTE? What is MERGE Statement? What is Filtered Index? Which are the New Data Types Introduced in SQL SERVER 2008? SQL SERVER – Interview Questions and Answers – Frequently Asked Questions – Day 16 of 31 What are the Advantages of Using CTE? How can we Rewrite Sub-Queries into Simple Select Statements or with Joins? What is CLR? What are Synonyms? What is LINQ? What are Isolation Levels? What is Use of EXCEPT Clause? What is XPath? What is NOLOCK? What is the Difference between Update Lock and Exclusive Lock? SQL SERVER – Interview Questions and Answers – Frequently Asked Questions – Day 17 of 31 How will you Handle Error in SQL SERVER 2008? What is RAISEERROR? What is RAISEERROR? How to Rebuild the Master Database? What is the XML Datatype? What is Data Compression? What is Use of DBCC Commands? How to Copy the Tables, Schema and Views from one SQL Server to Another? How to Find Tables without Indexes? SQL SERVER – Interview Questions and Answers – Frequently Asked Questions – Day 18 of 31 How to Copy Data from One Table to Another Table? What is Catalog Views? What is PIVOT and UNPIVOT? What is a Filestream? What is SQLCMD? What do you mean by TABLESAMPLE? What is ROW_NUMBER()? What are Ranking Functions? What is Change Data Capture (CDC) in SQL Server 2008? SQL SERVER – Interview Questions and Answers – Frequently Asked Questions – Day 19 of 31 How can I Track the Changes or Identify the Latest Insert-Update-Delete from a Table? What is the CPU Pressure? How can I Get Data from a Database on Another Server? What is the Bookmark Lookup and RID Lookup? What is Difference between ROLLBACK IMMEDIATE and WITH NO_WAIT during ALTER DATABASE? What is Difference between GETDATE and SYSDATETIME in SQL Server 2008? How can I Check that whether Automatic Statistic Update is Enabled or not? How to Find Index Size for Each Index on Table? What is the Difference between Seek Predicate and Predicate? What are Basics of Policy Management? What are the Advantages of Policy Management? SQL SERVER – Interview Questions and Answers – Frequently Asked Questions – Day 20 of 31 What are Policy Management Terms? What is the ‘FILLFACTOR’? Where in MS SQL Server is ’100’ equal to ‘0’? What are Points to Remember while Using the FILLFACTOR Argument? What is a ROLLUP Clause? What are Various Limitations of the Views? What is a Covered index? When I Delete any Data from a Table, does the SQL Server reduce the size of that table? What are Wait Types? How to Stop Log File Growing too Big? If any Stored Procedure is Encrypted, then can we see its definition in Activity Monitor? 2012 Example of Width Sensitive and Width Insensitive Collation Width Sensitive Collation: A single-byte character (half-width) represented as single-byte and the same character represented as a double-byte character (full-width) are when compared are not equal the collation is width sensitive. In this example we have one table with two columns. One column has a collation of width sensitive and the second column has a collation of width insensitive. Find Column Used in Stored Procedure – Search Stored Procedure for Column Name Very interesting conversation about how to find column used in a stored procedure. There are two different characters in the story and both are having a conversation about how to find column in the stored procedure. Here are two part story Part 1 | Part 2 SQL SERVER – 2012 Functions – FORMAT() and CONCAT() – An Interesting Usage Generate Script for Schema and Data – SQL in Sixty Seconds #021 – Video In simple words, in many cases the database move from one place to another place. It is not always possible to back up and restore databases. There are possibilities when only part of the database (with schema and data) has to be moved. In this video we learn that we can easily generate script for schema for data and move from one server to another one. INFORMATION_SCHEMA.COLUMNS and Value Character Maximum Length -1 I often see the value -1 in the CHARACTER_MAXIMUM_LENGTH column of INFORMATION_SCHEMA.COLUMNS table. I understand that the length of any column can be between 0 to large number but I do not get it when I see value in negative (i.e. -1). Any insight on this subject? Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Memory Lane, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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• Spooling in SQL execution plans

  - by Rob Farley

  Sewing has never been my thing. I barely even know the terminology, and when discussing this with American friends, I even found out that half the words that Americans use are different to the words that English and Australian people use. That said – let’s talk about spools! In particular, the Spool operators that you find in some SQL execution plans. This post is for T-SQL Tuesday, hosted this month by me! I’ve chosen to write about spools because they seem to get a bad rap (even in my song I used the line “There’s spooling from a CTE, they’ve got recursion needlessly”). I figured it was worth covering some of what spools are about, and hopefully explain why they are remarkably necessary, and generally very useful. If you have a look at the Books Online page about Plan Operators, at http://msdn.microsoft.com/en-us/library/ms191158.aspx, and do a search for the word ‘spool’, you’ll notice it says there are 46 matches. 46! Yeah, that’s what I thought too... Spooling is mentioned in several operators: Eager Spool, Lazy Spool, Index Spool (sometimes called a Nonclustered Index Spool), Row Count Spool, Spool, Table Spool, and Window Spool (oh, and Cache, which is a special kind of spool for a single row, but as it isn’t used in SQL 2012, I won’t describe it any further here). Spool, Table Spool, Index Spool, Window Spool and Row Count Spool are all physical operators, whereas Eager Spool and Lazy Spool are logical operators, describing the way that the other spools work. For example, you might see a Table Spool which is either Eager or Lazy. A Window Spool can actually act as both, as I’ll mention in a moment. In sewing, cotton is put onto a spool to make it more useful. You might buy it in bulk on a cone, but if you’re going to be using a sewing machine, then you quite probably want to have it on a spool or bobbin, which allows it to be used in a more effective way. This is the picture that I want you to think about in relation to your data. I’m sure you use spools every time you use your sewing machine. I know I do. I can’t think of a time when I’ve got out my sewing machine to do some sewing and haven’t used a spool. However, I often run SQL queries that don’t use spools. You see, the data that is consumed by my query is typically in a useful state without a spool. It’s like I can just sew with my cotton despite it not being on a spool! Many of my favourite features in T-SQL do like to use spools though. This looks like a very similar query to before, but includes an OVER clause to return a column telling me the number of rows in my data set. I’ll describe what’s going on in a few paragraphs’ time. So what does a Spool operator actually do? The spool operator consumes a set of data, and stores it in a temporary structure, in the tempdb database. This structure is typically either a Table (ie, a heap), or an Index (ie, a b-tree). If no data is actually needed from it, then it could also be a Row Count spool, which only stores the number of rows that the spool operator consumes. A Window Spool is another option if the data being consumed is tightly linked to windows of data, such as when the ROWS/RANGE clause of the OVER clause is being used. You could maybe think about the type of spool being like whether the cotton is going onto a small bobbin to fit in the base of the sewing machine, or whether it’s a larger spool for the top. A Table or Index Spool is either Eager or Lazy in nature. Eager and Lazy are Logical operators, which talk more about the behaviour, rather than the physical operation. If I’m sewing, I can either be all enthusiastic and get all my cotton onto the spool before I start, or I can do it as I need it. “Lazy” might not the be the best word to describe a person – in the SQL world it describes the idea of either fetching all the rows to build up the whole spool when the operator is called (Eager), or populating the spool only as it’s needed (Lazy). Window Spools are both physical and logical. They’re eager on a per-window basis, but lazy between windows. And when is it needed? The way I see it, spools are needed for two reasons. 1 – When data is going to be needed AGAIN. 2 – When data needs to be kept away from the original source. If you’re someone that writes long stored procedures, you are probably quite aware of the second scenario. I see plenty of stored procedures being written this way – where the query writer populates a temporary table, so that they can make updates to it without risking the original table. SQL does this too. Imagine I’m updating my contact list, and some of my changes move data to later in the book. If I’m not careful, I might update the same row a second time (or even enter an infinite loop, updating it over and over). A spool can make sure that I don’t, by using a copy of the data. This problem is known as the Halloween Effect (not because it’s spooky, but because it was discovered in late October one year). As I’m sure you can imagine, the kind of spool you’d need to protect against the Halloween Effect would be eager, because if you’re only handling one row at a time, then you’re not providing the protection... An eager spool will block the flow of data, waiting until it has fetched all the data before serving it up to the operator that called it. In the query below I’m forcing the Query Optimizer to use an index which would be upset if the Name column values got changed, and we see that before any data is fetched, a spool is created to load the data into. This doesn’t stop the index being maintained, but it does mean that the index is protected from the changes that are being done. There are plenty of times, though, when you need data repeatedly. Consider the query I put above. A simple join, but then counting the number of rows that came through. The way that this has executed (be it ideal or not), is to ask that a Table Spool be populated. That’s the Table Spool operator on the top row. That spool can produce the same set of rows repeatedly. This is the behaviour that we see in the bottom half of the plan. In the bottom half of the plan, we see that the a join is being done between the rows that are being sourced from the spool – one being aggregated and one not – producing the columns that we need for the query. Table v Index When considering whether to use a Table Spool or an Index Spool, the question that the Query Optimizer needs to answer is whether there is sufficient benefit to storing the data in a b-tree. The idea of having data in indexes is great, but of course there is a cost to maintaining them. Here we’re creating a temporary structure for data, and there is a cost associated with populating each row into its correct position according to a b-tree, as opposed to simply adding it to the end of the list of rows in a heap. Using a b-tree could even result in page-splits as the b-tree is populated, so there had better be a reason to use that kind of structure. That all depends on how the data is going to be used in other parts of the plan. If you’ve ever thought that you could use a temporary index for a particular query, well this is it – and the Query Optimizer can do that if it thinks it’s worthwhile. It’s worth noting that just because a Spool is populated using an Index Spool, it can still be fetched using a Table Spool. The details about whether or not a Spool used as a source shows as a Table Spool or an Index Spool is more about whether a Seek predicate is used, rather than on the underlying structure. Recursive CTE I’ve already shown you an example of spooling when the OVER clause is used. You might see them being used whenever you have data that is needed multiple times, and CTEs are quite common here. With the definition of a set of data described in a CTE, if the query writer is leveraging this by referring to the CTE multiple times, and there’s no simplification to be leveraged, a spool could theoretically be used to avoid reapplying the CTE’s logic. Annoyingly, this doesn’t happen. Consider this query, which really looks like it’s using the same data twice. I’m creating a set of data (which is completely deterministic, by the way), and then joining it back to itself. There seems to be no reason why it shouldn’t use a spool for the set described by the CTE, but it doesn’t. On the other hand, if we don’t pull as many columns back, we might see a very different plan. You see, CTEs, like all sub-queries, are simplified out to figure out the best way of executing the whole query. My example is somewhat contrived, and although there are plenty of cases when it’s nice to give the Query Optimizer hints about how to execute queries, it usually doesn’t do a bad job, even without spooling (and you can always use a temporary table). When recursion is used, though, spooling should be expected. Consider what we’re asking for in a recursive CTE. We’re telling the system to construct a set of data using an initial query, and then use set as a source for another query, piping this back into the same set and back around. It’s very much a spool. The analogy of cotton is long gone here, as the idea of having a continual loop of cotton feeding onto a spool and off again doesn’t quite fit, but that’s what we have here. Data is being fed onto the spool, and getting pulled out a second time when the spool is used as a source. (This query is running on AdventureWorks, which has a ManagerID column in HumanResources.Employee, not AdventureWorks2012) The Index Spool operator is sucking rows into it – lazily. It has to be lazy, because at the start, there’s only one row to be had. However, as rows get populated onto the spool, the Table Spool operator on the right can return rows when asked, ending up with more rows (potentially) getting back onto the spool, ready for the next round. (The Assert operator is merely checking to see if we’ve reached the MAXRECURSION point – it vanishes if you use OPTION (MAXRECURSION 0), which you can try yourself if you like). Spools are useful. Don’t lose sight of that. Every time you use temporary tables or table variables in a stored procedure, you’re essentially doing the same – don’t get upset at the Query Optimizer for doing so, even if you think the spool looks like an expensive part of the query. I hope you’re enjoying this T-SQL Tuesday. Why not head over to my post that is hosting it this month to read about some other plan operators? At some point I’ll write a summary post – once I have you should find a comment below pointing at it. @rob_farley

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• Performance Enhancement in Full-Text Search Query

  - by Calvin Sun

  Ever since its first release, we are continuing consolidating and developing InnoDB Full-Text Search feature. There is one recent improvement that worth blogging about. It is an effort with MySQL Optimizer team that simplifies some common queries’ Query Plans and dramatically shorted the query time. I will describe the issue, our solution and the end result by some performance numbers to demonstrate our efforts in continuing enhancement the Full-Text Search capability. The Issue: As we had discussed in previous Blogs, InnoDB implements Full-Text index as reversed auxiliary tables. The query once parsed will be reinterpreted into several queries into related auxiliary tables and then results are merged and consolidated to come up with the final result. So at the end of the query, we’ll have all matching records on hand, sorted by their ranking or by their Doc IDs. Unfortunately, MySQL’s optimizer and query processing had been initially designed for MyISAM Full-Text index, and sometimes did not fully utilize the complete result package from InnoDB. Here are a couple examples: Case 1: Query result ordered by Rank with only top N results: mysql> SELECT FTS_DOC_ID, MATCH (title, body) AGAINST ('database') AS SCORE FROM articles ORDER BY score DESC LIMIT 1; In this query, user tries to retrieve a single record with highest ranking. It should have a quick answer once we have all the matching documents on hand, especially if there are ranked. However, before this change, MySQL would almost retrieve rankings for almost every row in the table, sort them and them come with the top rank result. This whole retrieve and sort is quite unnecessary given the InnoDB already have the answer. In a real life case, user could have millions of rows, so in the old scheme, it would retrieve millions of rows' ranking and sort them, even if our FTS already found there are two 3 matched rows. Apparently, the million ranking retrieve is done in vain. In above case, it should just ask for 3 matched rows' ranking, all other rows' ranking are 0. If it want the top ranking, then it can just get the first record from our already sorted result. Case 2: Select Count(*) on matching records: mysql> SELECT COUNT(*) FROM articles WHERE MATCH (title,body) AGAINST ('database' IN NATURAL LANGUAGE MODE); In this case, InnoDB search can find matching rows quickly and will have all matching rows. However, before our change, in the old scheme, every row in the table was requested by MySQL one by one, just to check whether its ranking is larger than 0, and later comes up a count. In fact, there is no need for MySQL to fetch all rows, instead InnoDB already had all the matching records. The only thing need is to call an InnoDB API to retrieve the count The difference can be huge. Following query output shows how big the difference can be: mysql> select count(*) from searchindex_inno where match(si_title, si_text) against ('people')  +----------+ | count(*) | +----------+ | 666877 | +----------+ 1 row in set (16 min 17.37 sec) So the query took almost 16 minutes. Let’s see how long the InnoDB can come up the result. In InnoDB, you can obtain extra diagnostic printout by turning on “innodb_ft_enable_diag_print”, this will print out extra query info: Error log: keynr=2, 'people' NL search Total docs: 10954826 Total words: 0 UNION: Searching: 'people' Processing time: 2 secs: row(s) 666877: error: 10 ft_init() ft_init_ext() keynr=2, 'people' NL search Total docs: 10954826 Total words: 0 UNION: Searching: 'people' Processing time: 3 secs: row(s) 666877: error: 10 Output shows it only took InnoDB only 3 seconds to get the result, while the whole query took 16 minutes to finish. So large amount of time has been wasted on the un-needed row fetching. The Solution: The solution is obvious. MySQL can skip some of its steps, optimize its plan and obtain useful information directly from InnoDB. Some of savings from doing this include: 1) Avoid redundant sorting. Since InnoDB already sorted the result according to ranking. MySQL Query Processing layer does not need to sort to get top matching results. 2) Avoid row by row fetching to get the matching count. InnoDB provides all the matching records. All those not in the result list should all have ranking of 0, and no need to be retrieved. And InnoDB has a count of total matching records on hand. No need to recount. 3) Covered index scan. InnoDB results always contains the matching records' Document ID and their ranking. So if only the Document ID and ranking is needed, there is no need to go to user table to fetch the record itself. 4) Narrow the search result early, reduce the user table access. If the user wants to get top N matching records, we do not need to fetch all matching records from user table. We should be able to first select TOP N matching DOC IDs, and then only fetch corresponding records with these Doc IDs. Performance Results and comparison with MyISAM The result by this change is very obvious. I includes six testing result performed by Alexander Rubin just to demonstrate how fast the InnoDB query now becomes when comparing MyISAM Full-Text Search. These tests are base on the English Wikipedia data of 5.4 Million rows and approximately 16G table. The test was performed on a machine with 1 CPU Dual Core, SSD drive, 8G of RAM and InnoDB_buffer_pool is set to 8 GB. Table 1: SELECT with LIMIT CLAUSE mysql> SELECT si_title, match(si_title, si_text) against('family') as rel FROM si WHERE match(si_title, si_text) against('family') ORDER BY rel desc LIMIT 10; InnoDB MyISAM Times Faster Time for the query 1.63 sec 3 min 26.31 sec 127 You can see for this particular query (retrieve top 10 records), InnoDB Full-Text Search is now approximately 127 times faster than MyISAM. Table 2: SELECT COUNT QUERY mysql>select count(*) from si where match(si_title, si_text) against('family‘); +----------+ | count(*) | +----------+ | 293955 | +----------+ InnoDB MyISAM Times Faster Time for the query 1.35 sec 28 min 59.59 sec 1289 In this particular case, where there are 293k matching results, InnoDB took only 1.35 second to get all of them, while take MyISAM almost half an hour, that is about 1289 times faster!. Table 3: SELECT ID with ORDER BY and LIMIT CLAUSE for selected terms mysql> SELECT <ID>, match(si_title, si_text) against(<TERM>) as rel FROM si_<TB> WHERE match(si_title, si_text) against (<TERM>) ORDER BY rel desc LIMIT 10; Term InnoDB (time to execute) MyISAM(time to execute) Times Faster family 0.5 sec 5.05 sec 10.1 family film 0.95 sec 25.39 sec 26.7 Pizza restaurant orange county California 0.93 sec 32.03 sec 34.4 President united states of America 2.5 sec 36.98 sec 14.8 Table 4: SELECT title and text with ORDER BY and LIMIT CLAUSE for selected terms mysql> SELECT <ID>, si_title, si_text, ... as rel FROM si_<TB> WHERE match(si_title, si_text) against (<TERM>) ORDER BY rel desc LIMIT 10; Term InnoDB (time to execute) MyISAM(time to execute) Times Faster family 0.61 sec 41.65 sec 68.3 family film 1.15 sec 47.17 sec 41.0 Pizza restaurant orange county california 1.03 sec 48.2 sec 46.8 President united states of america 2.49 sec 44.61 sec 17.9 Table 5: SELECT ID with ORDER BY and LIMIT CLAUSE for selected terms mysql> SELECT <ID>, match(si_title, si_text) against(<TERM>) as rel  FROM si_<TB> WHERE match(si_title, si_text) against (<TERM>) ORDER BY rel desc LIMIT 10; Term InnoDB (time to execute) MyISAM(time to execute) Times Faster family 0.5 sec 5.05 sec 10.1 family film 0.95 sec 25.39 sec 26.7 Pizza restaurant orange county califormia 0.93 sec 32.03 sec 34.4 President united states of america 2.5 sec 36.98 sec 14.8 Table 6: SELECT COUNT(*) mysql> SELECT count(*) FROM si_<TB> WHERE match(si_title, si_text) against (<TERM>) LIMIT 10; Term InnoDB (time to execute) MyISAM(time to execute) Times Faster family 0.47 sec 82 sec 174.5 family film 0.83 sec 131 sec 157.8 Pizza restaurant orange county califormia 0.74 sec 106 sec 143.2 President united states of america 1.96 sec 220 sec 112.2  Again, table 3 to table 6 all showing InnoDB consistently outperform MyISAM in these queries by a large margin. It becomes obvious the InnoDB has great advantage over MyISAM in handling large data search. Summary: These results demonstrate the great performance we could achieve by making MySQL optimizer and InnoDB Full-Text Search more tightly coupled. I think there are still many cases that InnoDB’s result info have not been fully taken advantage of, which means we still have great room to improve. And we will continuously explore the area, and get more dramatic results for InnoDB full-text searches. Jimmy Yang, September 29, 2012

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• SQL SERVER – Weekly Series – Memory Lane – #037

  - by Pinal Dave

  Here is the list of selected articles of SQLAuthority.com across all these years. Instead of just listing all the articles I have selected a few of my most favorite articles and have listed them here with additional notes below it. Let me know which one of the following is your favorite article from memory lane. 2007 Convert Text to Numbers (Integer) – CAST and CONVERT If table column is VARCHAR and has all the numeric values in it, it can be retrieved as Integer using CAST or CONVERT function. List All Stored Procedure Modified in Last N Days If SQL Server suddenly start behaving in un-expectable behavior and if stored procedure were changed recently, following script can be used to check recently modified stored procedure. If a stored procedure was created but never modified afterwards modified date and create a date for that stored procedure are same. Count Duplicate Records – Rows Validate Field For DATE datatype using function ISDATE() We always checked DATETIME field for incorrect data type. One of the user input date as 30/2/2007. The date was sucessfully inserted in the temp table but while inserting from temp table to final table it crashed with error. We had now task to validate incorrect date value before we insert in final table. Jr. Developer asked me how can he do that? We check for incorrect data type (varchar, int, NULL) but this is incorrect date value. Regular expression works fine with them because of mm/dd/yyyy format. 2008 Find Space Used For Any Particular Table It is very simple to find out the space used by any table in the database. Two Convenient Features Inline Assignment – Inline Operations Here is the script which does both – Inline Assignment and Inline Operation DECLARE @idx INT = 0 SET @idx+=1 SELECT @idx Introduction to SPARSE Columns SPARSE column are better at managing NULL and ZERO values in SQL Server. It does not take any space in database at all. If column is created with SPARSE clause with it and it contains ZERO or NULL it will be take lesser space then regular column (without SPARSE clause). SP_CONFIGURE – Displays or Changes Global Configuration Settings If advanced settings are not enabled at configuration level SQL Server will not let user change the advanced features on server. Authorized user can turn on or turn off advance settings. 2009 Standby Servers and Types of Standby Servers Standby Server is a type of server that can be brought online in a situation when Primary Server goes offline and application needs continuous (high) availability of the server. There is always a need to set up a mechanism where data and objects from primary server are moved to secondary (standby) server. BLOB – Pointer to Image, Image in Database, FILESTREAM Storage When it comes to storing images in database there are two common methods. I had previously blogged about the same subject on my visit to Toronto. With SQL Server 2008, we have a new method of FILESTREAM storage. However, the answer on when to use FILESTREAM and when to use other methods is still vague in community. 2010 Upper Case Shortcut SQL Server Management Studio I select the word and hit CTRL+SHIFT+U and it SSMS immediately changes the case of the selected word. Similar way if one want to convert cases to lower case, another short cut CTRL+SHIFT+L is also available. The Self Join – Inner Join and Outer Join Self Join has always been a noteworthy case. It is interesting to ask questions about self join in a room full of developers. I often ask – if there are three kinds of joins, i.e.- Inner Join, Outer Join and Cross Join; what type of join is Self Join? The usual answer is that it is an Inner Join. However, the reality is very different. Parallelism – Row per Processor – Row per Thread – Thread 0  If you look carefully in the Properties window or XML Plan, there is “Thread 0?. What does this “Thread 0” indicate? Well find out from the blog post. How do I Learn and How do I Teach The blog post has raised three very interesting questions. How do you learn? How do you teach? What are you learning or teaching? Let me try to answer the same. 2011 SQL SERVER – Interview Questions and Answers – Frequently Asked Questions – Day 7 of 31 What are Different Types of Locks? What are Pessimistic Lock and Optimistic Lock? When is the use of UPDATE_STATISTICS command? What is the Difference between a HAVING clause and a WHERE clause? What is Connection Pooling and why it is Used? What are the Properties and Different Types of Sub-Queries? What are the Authentication Modes in SQL Server? How can it be Changed? SQL SERVER – Interview Questions and Answers – Frequently Asked Questions – Day 8 of 31 Which Command using Query Analyzer will give you the Version of SQL Server and Operating System? What is an SQL Server Agent? Can a Stored Procedure call itself or a Recursive Stored Procedure? How many levels of SP nesting is possible? What is Log Shipping? Name 3 ways to get an Accurate Count of the Number of Records in a Table? What does it mean to have QUOTED_IDENTIFIER ON? What are the Implications of having it OFF? What is the Difference between a Local and a Global Temporary Table? What is the STUFF Function and How Does it Differ from the REPLACE Function? What is PRIMARY KEY? What is UNIQUE KEY Constraint? What is FOREIGN KEY? SQL SERVER – Interview Questions and Answers – Frequently Asked Questions – Day 9 of 31 What is CHECK Constraint? What is NOT NULL Constraint? What is the difference between UNION and UNION ALL? What is B-Tree? How to get @@ERROR and @@ROWCOUNT at the Same Time? What is a Scheduled Job or What is a Scheduled Task? What are the Advantages of Using Stored Procedures? What is a Table Called, if it has neither Cluster nor Non-cluster Index? What is it Used for? Can SQL Servers Linked to other Servers like Oracle? What is BCP? When is it Used? SQL SERVER – Interview Questions and Answers – Frequently Asked Questions – Day 10 of 31 What Command do we Use to Rename a db, a Table and a Column? What are sp_configure Commands and SET Commands? How to Implement One-to-One, One-to-Many and Many-to-Many Relationships while Designing Tables? What is Difference between Commit and Rollback when Used in Transactions? What is an Execution Plan? When would you Use it? How would you View the Execution Plan? SQL SERVER – Interview Questions and Answers – Frequently Asked Questions – Day 11 of 31 What is Difference between Table Aliases and Column Aliases? Do they Affect Performance? What is the difference between CHAR and VARCHAR Datatypes? What is the Difference between VARCHAR and VARCHAR(MAX) Datatypes? What is the Difference between VARCHAR and NVARCHAR datatypes? Which are the Important Points to Note when Multilanguage Data is Stored in a Table? How to Optimize Stored Procedure Optimization? What is SQL Injection? How to Protect Against SQL Injection Attack? How to Find Out the List Schema Name and Table Name for the Database? What is CHECKPOINT Process in the SQL Server? SQL SERVER – Interview Questions and Answers – Frequently Asked Questions – Day 12 of 31 How does Using a Separate Hard Drive for Several Database Objects Improves Performance Right Away? How to Find the List of Fixed Hard Drive and Free Space on Server? Why can there be only one Clustered Index and not more than one? What is Difference between Line Feed (\n) and Carriage Return (\r)? Is It Possible to have Clustered Index on Separate Drive From Original Table Location? What is a Hint? How to Delete Duplicate Rows? Why the Trigger Fires Multiple Times in Single Login? 2012 CTRL+SHIFT+] Shortcut to Select Code Between Two Parenthesis Shortcut key is CTRL+SHIFT+]. This key can be very useful when dealing with multiple subqueries, CTE or query with multiple parentheses. When exercised this shortcut key it selects T-SQL code between two parentheses. Monday Morning Puzzle – Query Returns Results Sometimes but Not Always I am beginner with SQL Server. I have one query, it sometime returns a result and sometime it does not return me the result. Where should I start looking for a solution and what kind of information I should send to you so you can help me with solving. I have no clue, please guide me. Remove Debug Button in SSMS – SQL in Sixty Seconds #020 – Video Effect of Case Sensitive Collation on Resultset Collation is a very interesting concept but I quite often see it is heavily neglected. I have seen developer and DBA looking for a workaround to fix collation error rather than understanding if the side effect of the workaround. Switch Between Two Parenthesis using Shortcut CTRL+] Earlier this week I wrote a blog post about CTRL+SHIFT+] Shortcut to Select Code Between Two Parenthesis, I received quite a lot of positive feedback from readers. If you are a regular reader of the blog post, you must be aware that I appreciate the learning shared by readers. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Memory Lane, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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• Controlling what data populates STAR

  - by user10747017

  Beginning with the Primavera Reporting Database 2.2\P6 Analytics 1.2 release, the first release that supported the P6 Extended Schema, a new ability was added to filter which projects could be included during an ETL run. In previous releases, all projects were included in an ETL run. Additionally, all projects with the option to enable publication are included in the ETL run by default.Because the reporting needs for P6 Extended Schema are different from those of STAR, you can define a filter that will limit the data that is included in the STAR schema. For example, your STAR schema can be filter to only include all projects in a specific Portfolio, or all projects with a project code assignment of 'For Analytics.'  Any criteria that can be defined in a Where clause and added to a view can be used to filter the projects included in the STAR schema. I highly suggest this approach when dealing with large databases. Unnecessary projects could cause the Extract portion of the ETL process to take longer. A table in STAR called etl_projectlist is the key for what projects are targeted during the ETL process. To setup the filter, perform the following steps:1. Connect to your Primavera P6 Project Management Database as Pxrptuser (extended schema owner) and create a new view:create or replace view star_project_viewasselect PROJECTOBJECTID objectidfrom projectportfolio pp, projectprojectportfolio pppwhere pp.objectid = ppp.PROJECTPORTFOLIOOBJECTIDand pp.name = 'STAR Projects'--The main field that MUST be selected in the view is the projectobjectid. Selecting any other field besides the projectobjectid will cause the view to be invalid and will not work. Any Where clause can be used, but projectobjectid is the key.2. In your STAR installation directory go the \res folder and edit the staretl.properties file.  Here you will define the view to be used.  Add the following line or update if exists:star.project.filter.ds1=star_project_view3. When running the  staretl.cmd or staretl.sh process the database link to Pxrtpuser will be accessed and this view will be used to populate the etl_projectlist table  with the appropriate projectobjectids as defined in the view created in step 1 above.

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• What is the reason for section 1 of LGPL and what is the implication for section 9.

  - by Roland Schulz

  Why was section 1 added to LGPLv3? My understanding of section 3&4 is, one can convey the combined work under any license and with no requirements from GPLv3 (besides those explicitly stated as requirements in LGPLv3 3&4). Given that, why is section 1 necessary. Wouldn't that sections 3&4 by themselves already imply anyhow what section 1 explicitly states? I assume that I'm missing something and section 1 isn't redundant. Assuming that, does this have implications for other sections in GPLv3? E.g. does conveying a covered work under sections 3&4 fall under the patent clause of section 10 of GPLv3? Why does section 1 not also state an exception for section 10? Put another way. Is the Eigen FAQ correct by stating: LGPL requires [for header only libraries] pretty much the same as the 2-clause BSD license. It it true that for conveying object files including material from LGPLv3 headers no GPLv3 patent clauses apply?

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• When someone deletes a shared data source in SSRS

  - by Rob Farley

  SQL Server Reporting Services plays nicely. You can have things in the catalogue that get shared. You can have Reports that have Links, Datasets that can be used across different reports, and Data Sources that can be used in a variety of ways too. So if you find that someone has deleted a shared data source, you potentially have a bit of a horror story going on. And this works for this month’s T-SQL Tuesday theme, hosted by Nick Haslam, who wants to hear about horror stories. I don’t write about LobsterPot client horror stories, so I’m writing about a situation that a fellow MVP friend asked me about recently instead. The best thing to do is to grab a recent backup of the ReportServer database, restore it somewhere, and figure out what’s changed. But of course, this isn’t always possible. And it’s much nicer to help someone with this kind of thing, rather than to be trying to fix it yourself when you’ve just deleted the wrong data source. Unfortunately, it lets you delete data sources, without trying to scream that the data source is shared across over 400 reports in over 100 folders, as was the case for my friend’s colleague. So, suddenly there’s a big problem – lots of reports are failing, and the time to turn it around is small. You probably know which data source has been deleted, but getting the shared data source back isn’t the hard part (that’s just a connection string really). The nasty bit is all the re-mapping, to get those 400 reports working again. I know from exploring this kind of stuff in the past that the ReportServer database (using its default name) has a table called dbo.Catalog to represent the catalogue, and that Reports are stored here. However, the information about what data sources these deployed reports are configured to use is stored in a different table, dbo.DataSource. You could be forgiven for thinking that shared data sources would live in this table, but they don’t – they’re catalogue items just like the reports. Let’s have a look at the structure of these two tables (although if you’re reading this because you have a disaster, feel free to skim past). Frustratingly, there doesn’t seem to be a Books Online page for this information, sorry about that. I’m also not going to look at all the columns, just ones that I find interesting enough to mention, and that are related to the problem at hand. These fields are consistent all the way through to SQL Server 2012 – there doesn’t seem to have been any changes here for quite a while. dbo.Catalog The Primary Key is ItemID. It’s a uniqueidentifier. I’m not going to comment any more on that. A minor nice point about using GUIDs in unfamiliar databases is that you can more easily figure out what’s what. But foreign keys are for that too… Path, Name and ParentID tell you where in the folder structure the item lives. Path isn’t actually required – you could’ve done recursive queries to get there. But as that would be quite painful, I’m more than happy for the Path column to be there. Path contains the Name as well, incidentally. Type tells you what kind of item it is. Some examples are 1 for a folder and 2 a report. 4 is linked reports, 5 is a data source, 6 is a report model. I forget the others for now (but feel free to put a comment giving the full list if you know it). Content is an image field, remembering that image doesn’t necessarily store images – these days we’d rather use varbinary(max), but even in SQL Server 2012, this field is still image. It stores the actual item definition in binary form, whether it’s actually an image, a report, whatever. LinkSourceID is used for Linked Reports, and has a self-referencing foreign key (allowing NULL, of course) back to ItemID. Parameter is an ntext field containing XML for the parameters of the report. Not sure why this couldn’t be a separate table, but I guess that’s just the way it goes. This field gets changed when the default parameters get changed in Report Manager. There is nothing in dbo.Catalog that describes the actual data sources that the report uses. The default data sources would be part of the Content field, as they are defined in the RDL, but when you deploy reports, you typically choose to NOT replace the data sources. Anyway, they’re not in this table. Maybe it was already considered a bit wide to throw in another ntext field, I’m not sure. They’re in dbo.DataSource instead. dbo.DataSource The Primary key is DSID. Yes it’s a uniqueidentifier... ItemID is a foreign key reference back to dbo.Catalog Fields such as ConnectionString, Prompt, UserName and Password do what they say on the tin, storing information about how to connect to the particular source in question. Link is a uniqueidentifier, which refers back to dbo.Catalog. This is used when a data source within a report refers back to a shared data source, rather than embedding the connection information itself. You’d think this should be enforced by foreign key, but it’s not. It does allow NULLs though. Flags this is an int, and I’ll come back to this. When a Data Source gets deleted out of dbo.Catalog, you might assume that it would be disallowed if there are references to it from dbo.DataSource. Well, you’d be wrong. And not because of the lack of a foreign key either. Deleting anything from the catalogue is done by calling a stored procedure called dbo.DeleteObject. You can look at the definition in there – it feels very much like the kind of Delete stored procedures that many people write, the kind of thing that means they don’t need to worry about allowing cascading deletes with foreign keys – because the stored procedure does the lot. Except that it doesn’t quite do that. If it deleted everything on a cascading delete, we’d’ve lost all the data sources as configured in dbo.DataSource, and that would be bad. This is fine if the ItemID from dbo.DataSource hooks in – if the report is being deleted. But if a shared data source is being deleted, you don’t want to lose the existence of the data source from the report. So it sets it to NULL, and it marks it as invalid. We see this code in that stored procedure. UPDATE [DataSource]    SET       [Flags] = [Flags] & 0x7FFFFFFD, -- broken link       [Link] = NULL FROM    [Catalog] AS C    INNER JOIN [DataSource] AS DS ON C.[ItemID] = DS.[Link] WHERE    (C.Path = @Path OR C.Path LIKE @Prefix ESCAPE '*') Unfortunately there’s no semi-colon on the end (but I’d rather they fix the ntext and image types first), and don’t get me started about using the table name in the UPDATE clause (it should use the alias DS). But there is a nice comment about what’s going on with the Flags field. What I’d LIKE it to do would be to set the connection information to a report-embedded copy of the connection information that’s in the shared data source, the one that’s about to be deleted. I understand that this would cause someone to lose the benefit of having the data sources configured in a central point, but I’d say that’s probably still slightly better than LOSING THE INFORMATION COMPLETELY. Sorry, rant over. I should log a Connect item – I’ll put that on my todo list. So it sets the Link field to NULL, and marks the Flags to tell you they’re broken. So this is your clue to fixing it. A bitwise AND with 0x7FFFFFFD is basically stripping out the ‘2’ bit from a number. So numbers like 2, 3, 6, 7, 10, 11, etc, whose binary representation ends in either 11 or 10 get turned into 0, 1, 4, 5, 8, 9, etc. We can test for it using a WHERE clause that matches the SET clause we’ve just used. I’d also recommend checking for Link being NULL and also having no ConnectionString. And join back to dbo.Catalog to get the path (including the name) of broken reports are – in case you get a surprise from a different data source being broken in the past. SELECT c.Path, ds.Name FROM dbo.[DataSource] AS ds JOIN dbo.[Catalog] AS c ON c.ItemID = ds.ItemID WHERE ds.[Flags] = ds.[Flags] & 0x7FFFFFFD AND ds.[Link] IS NULL AND ds.[ConnectionString] IS NULL; When I just ran this on my own machine, having deleted a data source to check my code, I noticed a Report Model in the list as well – so if you had thought it was just going to be reports that were broken, you’d be forgetting something. So to fix those reports, get your new data source created in the catalogue, and then find its ItemID by querying Catalog, using Path and Name to find it. And then use this value to fix them up. To fix the Flags field, just add 2. I prefer to use bitwise OR which should do the same. Use the OUTPUT clause to get a copy of the DSIDs of the ones you’re changing, just in case you need to revert something later after testing (doing it all in a transaction won’t help, because you’ll just lock out the table, stopping you from testing anything). UPDATE ds SET [Flags] = [Flags] | 2, [Link] = '3AE31CBA-BDB4-4FD1-94F4-580B7FAB939D' /*Insert your own GUID*/ OUTPUT deleted.Name, deleted.DSID, deleted.ItemID, deleted.Flags FROM dbo.[DataSource] AS ds JOIN dbo.[Catalog] AS c ON c.ItemID = ds.ItemID WHERE ds.[Flags] = ds.[Flags] & 0x7FFFFFFD AND ds.[Link] IS NULL AND ds.[ConnectionString] IS NULL; But please be careful. Your mileage may vary. And there’s no reason why 400-odd broken reports needs to be quite the nightmare that it could be. Really, it should be less than five minutes. @rob_farley

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• SQL SERVER – Weekly Series – Memory Lane – #005

  - by pinaldave

  Here is the list of curetted articles of SQLAuthority.com across all these years. Instead of just listing all the articles I have selected a few of my most favorite articles and have listed them here with additional notes below it. Let me know which one of the following is your favorite article from memory lane. 2006 SQL SERVER – Cursor to Kill All Process in Database I indeed wrote this cursor and when I often look back, I wonder how naive I was to write this. The reason for writing this cursor was to free up my database from any existing connection so I can do database operation. This worked fine but there can be a potentially big issue if there was any important transaction was killed by this process. There is another way to to achieve the same thing where we can use ALTER syntax to take database in single user mode. Read more about that over here and here. 2007 Rules of Third Normal Form and Normalization Advantage – 3NF The rules of 3NF are mentioned here Make a separate table for each set of related attributes, and give each table a primary key. If an attribute depends on only part of a multi-valued key, remove it to a separate table If attributes do not contribute to a description of the key, remove them to a separate table. Correct Syntax for Stored Procedure SP Sometime a simple question is the most important question. I often see in industry incorrectly written Stored Procedure. Few writes code after the most outer BEGIN…END and few writes code after the GO Statement. In this brief blog post, I have attempted to explain the same. 2008 Switch Between Result Pan and Query Pan – SQL Shortcut Many times when I am writing query I have to scroll the result displayed in the result set. Most of the developer uses the mouse to switch between and Query Pane and Result Pane. There are few developers who are crazy about Keyboard shortcuts. F6 is the keyword which can be used to switch between query pane and tabs of the result pane. Interesting Observation – Use of Index and Execution Plan Query Optimization is a complex game and it has its own rules. From the example in the article we have discovered that Query Optimizer does not use clustered index to retrieve data, sometime non clustered index provides optimal performance for retrieving Primary Key. When all the rows and columns are selected Primary Key should be used to select data as it provides optimal performance. 2009 Interesting Observation – TOP 100 PERCENT and ORDER BY If you pull up any application or system where there are more than 100 SQL Server Views are created – I am very confident that at one or two places you will notice the scenario wherein View the ORDER BY clause is used with TOP 100 PERCENT. SQL Server 2008 VIEW with ORDER BY clause does not throw an error; moreover, it does not acknowledge the presence of it as well. In this article we have taken three perfect examples and demonstrated which clause we should use when. Comma Separated Values (CSV) from Table Column A Very common question – How to create comma separated values from a table in the database? The answer is also very common if we use XML. Check out this article for quick learning on the same subject. Azure Start Guide – Step by Step Installation Guide Though Azure portal has changed a quite bit since I wrote this article, the concept used in this article are not old. They are still valid and many of the functions are still working as mentioned in the article. I believe this one article will put you on the track to use Azure! Size of Index Table for Each Index – Solution Earlier I have posted a small question on this blog and requested help from readers to participate here and provide a solution. The puzzle was to write a query that will return the size for each index that is on any particular table. We need a query that will return an additional column in the above listed query and it should contain the size of the index. This article presents two of the best solutions from the puzzle. 2010 Well, this week in 2010 was the week of puzzles as I posted three interesting puzzles. Till today I am noticing pretty good interesting in the puzzles. They are tricky but for sure brings a great value if you are a database developer for a long time. I suggest you go over this puzzles and their answers. Did you really know all of the answers? I am confident that reading following three blog post will for sure help you enhance the experience with T-SQL. SQL SERVER – Challenge – Puzzle – Usage of FAST Hint SQL SERVER – Puzzle – Challenge – Error While Converting Money to Decimal SQL SERVER – Challenge – Puzzle – Why does RIGHT JOIN Exists 2011 DVM sys.dm_os_sys_info Column Name Changed in SQL Server 2012 Have you ever faced a situation where something does not work? When you try to fix it - you enjoy fixing it and started to appreciate the breaking changes. Well, this was exactly I felt yesterday. Before I begin my story, I want to candidly state that I do not encourage anybody to use * in the SELECT statement. Now the disclaimer is over – I suggest you read the original story – you will love it! Get Directory Structure using Extended Stored Procedure xp_dirtree Here is the question to you – why would you do something in SQL Server where you can do the same task in command prompt much easily. Well, the answer is sometime there are real use cases when we have to do such thing. This is a similar example where I have demonstrated how in SQL Server 2012 we can use extended stored procedure to retrieve directory structure. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Memory Lane, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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• Null Values And The T-SQL IN Operator

  - by Jesse

  I came across some unexpected behavior while troubleshooting a failing test the other day that took me long enough to figure out that I thought it was worth sharing here. I finally traced the failing test back to a SELECT statement in a stored procedure that was using the IN t-sql operator to exclude a certain set of values. Here’s a very simple example table to illustrate the issue: Customers CustomerId INT, NOT NULL, Primary Key CustomerName nvarchar(100) NOT NULL SalesRegionId INT NULL   The ‘SalesRegionId’ column contains a number representing the sales region that the customer belongs to. This column is nullable because new customers get created all the time but assigning them to sales regions is a process that is handled by a regional manager on a periodic basis. For the purposes of this example, the Customers table currently has the following rows: CustomerId CustomerName SalesRegionId 1 Customer A 1 2 Customer B NULL 3 Customer C 4 4 Customer D 2 5 Customer E 3   How could we write a query against this table for all customers that are NOT in sales regions 2 or 4? You might try something like this: 1: SELECT 2: CustomerId, 3: CustomerName, 4: SalesRegionId 5: FROM Customers 6: WHERE SalesRegionId NOT IN (2,4)   Will this work? In short, no; at least not in the way that you might expect. Here’s what this query will return given the example data we’re working with: CustomerId CustomerName SalesRegionId 1 Customer A 1 5 Customer E 5   I was expecting that this query would also return ‘Customer B’, since that customer has a NULL SalesRegionId. In my mind, having a customer with no sales region should be included in a set of customers that are not in sales regions 2 or 4.When I first started troubleshooting my issue I made note of the fact that this query should probably be re-written without the NOT IN clause, but I didn’t suspect that the NOT IN clause was actually the source of the issue. This particular query was only one minor piece in a much larger process that was being exercised via an automated integration test and I simply made a poor assumption that the NOT IN would work the way that I thought it should. So why doesn’t this work the way that I thought it should? From the MSDN documentation on the t-sql IN operator: If the value of test_expression is equal to any value returned by subquery or is equal to any expression from the comma-separated list, the result value is TRUE; otherwise, the result value is FALSE. Using NOT IN negates the subquery value or expression. The key phrase out of that quote is, “… is equal to any expression from the comma-separated list…”. The NULL SalesRegionId isn’t included in the NOT IN because of how NULL values are handled in equality comparisons. From the MSDN documentation on ANSI_NULLS: The SQL-92 standard requires that an equals (=) or not equal to (<>) comparison against a null value evaluates to FALSE. When SET ANSI_NULLS is ON, a SELECT statement using WHERE column_name = NULL returns zero rows even if there are null values in column_name. A SELECT statement using WHERE column_name <> NULL returns zero rows even if there are nonnull values in column_name. In fact, the MSDN documentation on the IN operator includes the following blurb about using NULL values in IN sub-queries or expressions that are used with the IN operator: Any null values returned by subquery or expression that are compared to test_expression using IN or NOT IN return UNKNOWN. Using null values in together with IN or NOT IN can produce unexpected results. If I were to include a ‘SET ANSI_NULLS OFF’ command right above my SELECT statement I would get ‘Customer B’ returned in the results, but that’s definitely not the right way to deal with this. We could re-write the query to explicitly include the NULL value in the WHERE clause: 1: SELECT 2: CustomerId, 3: CustomerName, 4: SalesRegionId 5: FROM Customers 6: WHERE (SalesRegionId NOT IN (2,4) OR SalesRegionId IS NULL)   This query works and properly includes ‘Customer B’ in the results, but I ultimately opted to re-write the query using a LEFT OUTER JOIN against a table variable containing all of the values that I wanted to exclude because, in my case, there could potentially be several hundred values to be excluded. If we were to apply the same refactoring to our simple sales region example we’d end up with: 1: DECLARE @regionsToIgnore TABLE (IgnoredRegionId INT) 2: INSERT @regionsToIgnore values (2),(4) 3:  4: SELECT 5: c.CustomerId, 6: c.CustomerName, 7: c.SalesRegionId 8: FROM Customers c 9: LEFT OUTER JOIN @regionsToIgnore r ON r.IgnoredRegionId = c.SalesRegionId 10: WHERE r.IgnoredRegionId IS NULL By performing a LEFT OUTER JOIN from Customers to the @regionsToIgnore table variable we can simply exclude any rows where the IgnoredRegionId is null, as those represent customers that DO NOT appear in the ignored regions list. This approach will likely perform better if the number of sales regions to ignore gets very large and it also will correctly include any customers that do not yet have a sales region.

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• SQL : where vs. on in join

  - by Erwin

  Perhaps a dumb question, but consider these 2 tables : T1 Store Year 01 2009 02 2009 03 2009 01 2010 02 2010 03 2010 T2 Store 02 Why is this INNER JOIN giving me the results I want (filtering the [year] in the ON clause) : select t1.* from t1 inner join t2 on t1.store = t2.store and t1.[year] = '2009' Store Year 02 2009 And why the LEFT OUTER JOIN include records of year 2010 ? select t1.* from t1 left outer join t2 on t1.store = t2.store and t1.year = '2009' where t2.store is null 01 2009 03 2009 01 2010 02 2010 03 2010 And I have to write the [year] filter in the 'WHERE' clause : select t1.* from t1 left outer join t2 on t1.store = t2.store where t2.store is null and t1.year = '2009' 01 2009 03 2009 Like I said, perhaps a dumb question, but it's bugging me !

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• Prevent SQL injection from form-generated SQL - NO PreparedStmts

  - by Markos Fragkakis

  Hi all, I have a search table where user will be able to filter results with a filter of the type: Field [Name], Value [John], Remove Rule Field [Surname], Value [Blake], Remove Rule Field [Has Children], Value [Yes], Remove Rule Add Rule So the user will be able to set an arbitrary set of filters, which will result essentially in a completely dynamic WHERE clause. In the future I will also have to implement more complicated logical expressions, like Where (name=John OR name=Nick) AND (surname=Blake OR surname=Bourne), Of all 10 fields the user may or may not filter by, I don't know how many and which filters the user will set. So, I cannot use a prepared statement (which assumes that at least we know the fields in the WHERE clause). This is why prepared statements are unfortunately out of the question, I have to do it with plain old, generated SQL. What measures can I take to protect the application from SQL Injection (REGEX-wise or any other way)?

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• Can't Set Crystal Report Selection Formula Programatically

  - by eidylon

  Hello all, first, I can't stand Crystal! Okay, that's off my chest... Now, we have an old VB6 app we maintain for a client, which uses the Crystal Automation library to programatically change the record selection formulas in a bunch of Crystal Reports 8.5 reports. There are two reports which are ALMOST identical. I had to change them recently to add another field from another table. When I added the table in to the reports though, while it added it in the visual designer, it did not add it in the FROM clause of the SQL statement. So, I manually edited the SQL statement to add in the additional join. KO, works great. If i run the reports in Crystal preview mode, they work exactly as expected. Now, the users went to test the changes from within the VB app. One of the reports works fine and dandy. The other report however, is failing to set the selection formula as expected. The code sets the selection formulas using the function PESetSelectionFormula. I verified that the string being passed in to the function as the new selection formula is correct via a step-through examination of the variables. The call to PESetSelectionFormula seems to be working okay, and is returning a value of 1, which as near as I can find anywhere indicates success. (The other report, which is working fine from code is also returning 1.) However, the report is failing with an error: Error Code: 534 - Error detected by database DLL. The code, for debugging purposes dumps out the SQL string currently being used by the report. The SQL coming out of the report is: SELECT ... FROM ... WHERE ORDER BY ... As you can see, the WHERE clause is blank, which I would imagine is why the database DLL is upchucking on this statement. I don't understand why the automation library is not setting the WHERE clause even though the call to PESetSelectionFormula is being passed a valid string and is returning success. I thought perhaps it was because I had manually edited the SQL in the report to add the table it wasn't adding, but I did the same thing in the other nearly identical report, and that one is working fine. Anyone have any ideas why PESetSelectionFormula might report success but not actually do anything? P.S. I have already tried doing a Database Verify Database from the menus, and that said the report was all up to date and did not help at all.

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• How to avoid the "divide by zero" error in SQL?

  - by Henrik Staun Poulsen

  I hate this error message: Msg 8134, Level 16, State 1, Line 1 Divide by zero error encountered. What is the best way to write SQL code, so that I will never see this error message again? I mean, I could add a where clause so that my divisor is never zero. Or I could add a case statement, so that there is a special treatment for zero. Is the best way to use a NullIf clause? Is there better way, or how can this be enforced?

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• How dynamic can I make my LINQ To SQL Statements?

  - by mcass20

  I have the need to construct a LINQ To SQL statement at runtime based on input from a user and I can't seem to figure out how to dynamically build the WHERE clause. I have no problem with the following: string Filters = "<value>FOO</value>"; Where("FormattedMessage.Contains(@0)",Filters) But what I really need is to make the entire WHERE clause dynamic. This way I can add multiple conditions at runtime like this (rough idea): foreach (Filter filter in filterlist) { whereclause = whereclause + "&& formattedmessage.contains(filter)"; }

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• How do I parse boolean logic?

  - by d03boy

  I need to write a boolean logic parser which will translate the boolean logic language to a SQL WHERE clause. The order of the operands will always be in the correct order (with value on the right). Here is a relatively simple example. There could be nested parentheses and the use of NOT operators, etc. (CACOUNT=01 OR CACOUNT=02 OR CACOUNT=03 OR CACOUNT=05 OR CACOUNT=07 OR CACOUNT=09 OR CACOUNT=12 OR CACOUNT=13 OR CACOUNT=18) AND Q4=1 AND NAME=TIMOTHY Here is what the WHERE clause would resemble. WHERE ( EXISTS ( SELECT 1 FROM MyVerticalTable b WHERE b.Key=a.Key AND b.Key='CACOUNT' AND b.Value='01' ) )

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• view and order by

  - by trojanwarrior3000

  why subquery of view can't have order by clause?

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• ADO.NET Entity Model and LINQ

  - by Richard

  Hi all I'm using an ADO.NET Entity Model which I'm trying to query using LINQ. The problem I'm having is that I can't specify the where clause as I'd like. For instance, consider the following query: AccountsDM db = new AccountsDM(ConfigurationManager.ConnectionStrings["PrimaryEF"].ConnectionString); var accounts = from a in db.Accounts select a; foreach (var account in accounts) { foreach (var ident in account.Identifiers) { if (ident.Identifier == identifier) { // ident.Identifier is what I'd like to be filtering in the WHERE clause below } } } Ideally, I'd like that to become: var accounts = from a in db.Accounts where a.Identifiers.Identifier == identifier select a; I'm guessing I've probably not set up my Entity Model correctly in VS2010. Any advice you can offer would be gratefully received. Thanks, Richard.

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• mysql view performance

  - by vamsivanka

  I have a table for about 100,000 users in it. First Case: explain select * from users where state = 'ca' when i do an explain plan for the above query i got the cost as 5200 Second Case: Create or replace view vw_users as select * from users Explain select * from vw_users where state = 'ca' when i do an explain plan on the second query i got the cost as 100,000. How does the where clause in the view work ?? Is the where clause applied after the view retrieves all the rows. Please let know, how can i fix this issue. Thanks

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• Prevent SQL injection from form-generated SQL.

  - by Markos Fragkakis

  Hi all, I have a search table where user will be able to filter results with a filter of the type: Field [Name], Value [John], Remove Rule Field [Surname], Value [Blake], Remove Rule Field [Has Children], Value [Yes], Remove Rule Add Rule So the user will be able to set an arbitrary set of filters, which will result essentially in a completely dynamic WHERE clause. In the future I will also have to implement more complicated logical expressions, like Where (name=John OR name=Nick) AND (surname=Blake OR surname=Bourne), Of all 10 fields the user may or may not filter by, I don't know how many and which filters the user will set. So, I cannot use a prepared statement (which assumes that at least we know the fields in the WHERE clause). This is why prepared statements are unfortunately out of the question, I have to do it with plain old, generated SQL. What measures can I take to protect the application from SQL Injection (REGEX-wise or any other way)?

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• Rails can't render polymorphic associations to XML?

  - by ambertch

  When I render XML with an :include clause for a polymorphic association I have, it doesn't work. I end up with the XML returning the object pointers instead of the actual objects, like: <posts> #<Comment:0x102ed1540>#<Comment:0x102ecaa38>#<Comment:0x102ec7fe0>#<Comment:0x102ec3cd8> </posts> Yet as_json works! When I render JSON with :include clause, the associations are rendered correctly and I get something like: posts":[ {"type":"Comment","created_at":"2010-04-20T23:02:30-07:00","id":7,"content":"fourth comment"}, {"type":"Comment","created_at":"2010-04-20T23:02:26-07:00","id":6,"content":"third comment"}] My current workaround is using XML builder, but I'm not too comfortable with that in the long run. Does anyone happen to know about this issue? I'm kind of in a catch-22 because while XML doesn't render the associations, as_json doesn't render in a kosher json format (returns an array rather than a list of hashes as proper json should) and the deserializer I'm using on the client side would require modification to parse the json correctly.

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• Legality, terms of service for performing a web crawl

  - by Berlin Brown

  I was going to crawl a site for some research I was collecting. But, apparently the terms of service is quite clear on the topic. Is it illegal to now "follow" the terms of service. And what can the site normally do? Here is an example clause in the TOS. Also, what about sites that don't provide this particular clause. Restrictions: "use any robot, spider, site search application, or other automated device, process or means to access, retrieve, scrape, or index the site" It is just research? Edit: "OK, from the standpoint of designing an efficient crawler. Should I provide some form of natural language engine to read terms of service and then abide by them."

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• Group by/count in LINQ against SQL Compact 3.5 SP2

  - by bash74

  Hello, I am using LINQ-To-Entities in C# and run queries against a SQL Compact Server 3.5 SP2. What I try to achieve is a simple group by with an additional where clause which includes a Count(). var baseIdent="expression"; var found=from o in ObservedElements where o.ObservedRoots.BaseIdent==baseIdent group o by o.ID into grouped where grouped.Count()==1 select new {key=grouped.Key, val=grouped}; foreach(var res in found){ //do something here } This query throws the famous exception "A parameter is not allowed in this location. Ensure that the '@' sign and all other parameters are in a valid location in the SQL statement." When I either omit the where clause OR directly enter the expression "expression" in the query (where o.ObservedRoots.BaseIdent=="expression") everything just works fine. Does anybody know how to solve this? Workaround would also be fine? Thanks in advance, Sebastian

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• Does a C# using statement perform try/finally?

  - by Lirik

  Suppose that I have the following code: private void UpdateDB(QuoteDataSet dataSet, Strint tableName) { using(SQLiteConnection conn = new SQLiteConnection(_connectionString)) { conn.Open(); using (SQLiteTransaction transaction = conn.BeginTransaction()) { using (SQLiteCommand cmd = new SQLiteCommand("SELECT * FROM " + tableName, conn)) { using (SQLiteDataAdapter sqliteAdapter = new SQLiteDataAdapter()) { sqliteAdapter.Update(dataSet, tableName); } } transaction.Commit(); } } } The C# documentation states that with a using statement the object within the scope will be disposed and I've seen several places where it's suggested that we don't need to use try/finally clause. I usually surround my connections with a try/finally, and I always close the connection in the finally clause. Given the above code, is it reasonable to assume that the connection will be closed if there is an exception?

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