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  • When is a SQL function not a function?

    - by Rob Farley
    Should SQL Server even have functions? (Oh yeah – this is a T-SQL Tuesday post, hosted this month by Brad Schulz) Functions serve an important part of programming, in almost any language. A function is a piece of code that is designed to return something, as opposed to a piece of code which isn’t designed to return anything (which is known as a procedure). SQL Server is no different. You can call stored procedures, even from within other stored procedures, and you can call functions and use these in other queries. Stored procedures might query something, and therefore ‘return data’, but a function in SQL is considered to have the type of the thing returned, and can be used accordingly in queries. Consider the internal GETDATE() function. SELECT GETDATE(), SomeDatetimeColumn FROM dbo.SomeTable; There’s no logical difference between the field that is being returned by the function and the field that’s being returned by the table column. Both are the datetime field – if you didn’t have inside knowledge, you wouldn’t necessarily be able to tell which was which. And so as developers, we find ourselves wanting to create functions that return all kinds of things – functions which look up values based on codes, functions which do string manipulation, and so on. But it’s rubbish. Ok, it’s not all rubbish, but it mostly is. And this isn’t even considering the SARGability impact. It’s far more significant than that. (When I say the SARGability aspect, I mean “because you’re unlikely to have an index on the result of some function that’s applied to a column, so try to invert the function and query the column in an unchanged manner”) I’m going to consider the three main types of user-defined functions in SQL Server: Scalar Inline Table-Valued Multi-statement Table-Valued I could also look at user-defined CLR functions, including aggregate functions, but not today. I figure that most people don’t tend to get around to doing CLR functions, and I’m going to focus on the T-SQL-based user-defined functions. Most people split these types of function up into two types. So do I. Except that most people pick them based on ‘scalar or table-valued’. I’d rather go with ‘inline or not’. If it’s not inline, it’s rubbish. It really is. Let’s start by considering the two kinds of table-valued function, and compare them. These functions are going to return the sales for a particular salesperson in a particular year, from the AdventureWorks database. CREATE FUNCTION dbo.FetchSales_inline(@salespersonid int, @orderyear int) RETURNS TABLE AS  RETURN (     SELECT e.LoginID as EmployeeLogin, o.OrderDate, o.SalesOrderID     FROM Sales.SalesOrderHeader AS o     LEFT JOIN HumanResources.Employee AS e     ON e.EmployeeID = o.SalesPersonID     WHERE o.SalesPersonID = @salespersonid     AND o.OrderDate >= DATEADD(year,@orderyear-2000,'20000101')     AND o.OrderDate < DATEADD(year,@orderyear-2000+1,'20000101') ) ; GO CREATE FUNCTION dbo.FetchSales_multi(@salespersonid int, @orderyear int) RETURNS @results TABLE (     EmployeeLogin nvarchar(512),     OrderDate datetime,     SalesOrderID int     ) AS BEGIN     INSERT @results (EmployeeLogin, OrderDate, SalesOrderID)     SELECT e.LoginID, o.OrderDate, o.SalesOrderID     FROM Sales.SalesOrderHeader AS o     LEFT JOIN HumanResources.Employee AS e     ON e.EmployeeID = o.SalesPersonID     WHERE o.SalesPersonID = @salespersonid     AND o.OrderDate >= DATEADD(year,@orderyear-2000,'20000101')     AND o.OrderDate < DATEADD(year,@orderyear-2000+1,'20000101')     ;     RETURN END ; GO You’ll notice that I’m being nice and responsible with the use of the DATEADD function, so that I have SARGability on the OrderDate filter. Regular readers will be hoping I’ll show what’s going on in the execution plans here. Here I’ve run two SELECT * queries with the “Show Actual Execution Plan” option turned on. Notice that the ‘Query cost’ of the multi-statement version is just 2% of the ‘Batch cost’. But also notice there’s trickery going on. And it’s nothing to do with that extra index that I have on the OrderDate column. Trickery. Look at it – clearly, the first plan is showing us what’s going on inside the function, but the second one isn’t. The second one is blindly running the function, and then scanning the results. There’s a Sequence operator which is calling the TVF operator, and then calling a Table Scan to get the results of that function for the SELECT operator. But surely it still has to do all the work that the first one is doing... To see what’s actually going on, let’s look at the Estimated plan. Now, we see the same plans (almost) that we saw in the Actuals, but we have an extra one – the one that was used for the TVF. Here’s where we see the inner workings of it. You’ll probably recognise the right-hand side of the TVF’s plan as looking very similar to the first plan – but it’s now being called by a stack of other operators, including an INSERT statement to be able to populate the table variable that the multi-statement TVF requires. And the cost of the TVF is 57% of the batch! But it gets worse. Let’s consider what happens if we don’t need all the columns. We’ll leave out the EmployeeLogin column. Here, we see that the inline function call has been simplified down. It doesn’t need the Employee table. The join is redundant and has been eliminated from the plan, making it even cheaper. But the multi-statement plan runs the whole thing as before, only removing the extra column when the Table Scan is performed. A multi-statement function is a lot more powerful than an inline one. An inline function can only be the result of a single sub-query. It’s essentially the same as a parameterised view, because views demonstrate this same behaviour of extracting the definition of the view and using it in the outer query. A multi-statement function is clearly more powerful because it can contain far more complex logic. But a multi-statement function isn’t really a function at all. It’s a stored procedure. It’s wrapped up like a function, but behaves like a stored procedure. It would be completely unreasonable to expect that a stored procedure could be simplified down to recognise that not all the columns might be needed, but yet this is part of the pain associated with this procedural function situation. The biggest clue that a multi-statement function is more like a stored procedure than a function is the “BEGIN” and “END” statements that surround the code. If you try to create a multi-statement function without these statements, you’ll get an error – they are very much required. When I used to present on this kind of thing, I even used to call it “The Dangers of BEGIN and END”, and yes, I’ve written about this type of thing before in a similarly-named post over at my old blog. Now how about scalar functions... Suppose we wanted a scalar function to return the count of these. CREATE FUNCTION dbo.FetchSales_scalar(@salespersonid int, @orderyear int) RETURNS int AS BEGIN     RETURN (         SELECT COUNT(*)         FROM Sales.SalesOrderHeader AS o         LEFT JOIN HumanResources.Employee AS e         ON e.EmployeeID = o.SalesPersonID         WHERE o.SalesPersonID = @salespersonid         AND o.OrderDate >= DATEADD(year,@orderyear-2000,'20000101')         AND o.OrderDate < DATEADD(year,@orderyear-2000+1,'20000101')     ); END ; GO Notice the evil words? They’re required. Try to remove them, you just get an error. That’s right – any scalar function is procedural, despite the fact that you wrap up a sub-query inside that RETURN statement. It’s as ugly as anything. Hopefully this will change in future versions. Let’s have a look at how this is reflected in an execution plan. Here’s a query, its Actual plan, and its Estimated plan: SELECT e.LoginID, y.year, dbo.FetchSales_scalar(p.SalesPersonID, y.year) AS NumSales FROM (VALUES (2001),(2002),(2003),(2004)) AS y (year) CROSS JOIN Sales.SalesPerson AS p LEFT JOIN HumanResources.Employee AS e ON e.EmployeeID = p.SalesPersonID; We see here that the cost of the scalar function is about twice that of the outer query. Nicely, the query optimizer has worked out that it doesn’t need the Employee table, but that’s a bit of a red herring here. There’s actually something way more significant going on. If I look at the properties of that UDF operator, it tells me that the Estimated Subtree Cost is 0.337999. If I just run the query SELECT dbo.FetchSales_scalar(281,2003); we see that the UDF cost is still unchanged. You see, this 0.0337999 is the cost of running the scalar function ONCE. But when we ran that query with the CROSS JOIN in it, we returned quite a few rows. 68 in fact. Could’ve been a lot more, if we’d had more salespeople or more years. And so we come to the biggest problem. This procedure (I don’t want to call it a function) is getting called 68 times – each one between twice as expensive as the outer query. And because it’s calling it in a separate context, there is even more overhead that I haven’t considered here. The cheek of it, to say that the Compute Scalar operator here costs 0%! I know a number of IT projects that could’ve used that kind of costing method, but that’s another story that I’m not going to go into here. Let’s look at a better way. Suppose our scalar function had been implemented as an inline one. Then it could have been expanded out like a sub-query. It could’ve run something like this: SELECT e.LoginID, y.year, (SELECT COUNT(*)     FROM Sales.SalesOrderHeader AS o     LEFT JOIN HumanResources.Employee AS e     ON e.EmployeeID = o.SalesPersonID     WHERE o.SalesPersonID = p.SalesPersonID     AND o.OrderDate >= DATEADD(year,y.year-2000,'20000101')     AND o.OrderDate < DATEADD(year,y.year-2000+1,'20000101')     ) AS NumSales FROM (VALUES (2001),(2002),(2003),(2004)) AS y (year) CROSS JOIN Sales.SalesPerson AS p LEFT JOIN HumanResources.Employee AS e ON e.EmployeeID = p.SalesPersonID; Don’t worry too much about the Scan of the SalesOrderHeader underneath a Nested Loop. If you remember from plenty of other posts on the matter, execution plans don’t push the data through. That Scan only runs once. The Index Spool sucks the data out of it and populates a structure that is used to feed the Stream Aggregate. The Index Spool operator gets called 68 times, but the Scan only once (the Number of Executions property demonstrates this). Here, the Query Optimizer has a full picture of what’s being asked, and can make the appropriate decision about how it accesses the data. It can simplify it down properly. To get this kind of behaviour from a function, we need it to be inline. But without inline scalar functions, we need to make our function be table-valued. Luckily, that’s ok. CREATE FUNCTION dbo.FetchSales_inline2(@salespersonid int, @orderyear int) RETURNS table AS RETURN (SELECT COUNT(*) as NumSales     FROM Sales.SalesOrderHeader AS o     LEFT JOIN HumanResources.Employee AS e     ON e.EmployeeID = o.SalesPersonID     WHERE o.SalesPersonID = @salespersonid     AND o.OrderDate >= DATEADD(year,@orderyear-2000,'20000101')     AND o.OrderDate < DATEADD(year,@orderyear-2000+1,'20000101') ); GO But we can’t use this as a scalar. Instead, we need to use it with the APPLY operator. SELECT e.LoginID, y.year, n.NumSales FROM (VALUES (2001),(2002),(2003),(2004)) AS y (year) CROSS JOIN Sales.SalesPerson AS p LEFT JOIN HumanResources.Employee AS e ON e.EmployeeID = p.SalesPersonID OUTER APPLY dbo.FetchSales_inline2(p.SalesPersonID, y.year) AS n; And now, we get the plan that we want for this query. All we’ve done is tell the function that it’s returning a table instead of a single value, and removed the BEGIN and END statements. We’ve had to name the column being returned, but what we’ve gained is an actual inline simplifiable function. And if we wanted it to return multiple columns, it could do that too. I really consider this function to be superior to the scalar function in every way. It does need to be handled differently in the outer query, but in many ways it’s a more elegant method there too. The function calls can be put amongst the FROM clause, where they can then be used in the WHERE or GROUP BY clauses without fear of calling the function multiple times (another horrible side effect of functions). So please. If you see BEGIN and END in a function, remember it’s not really a function, it’s a procedure. And then fix it. @rob_farley

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  • SQL Server, how to join a table in a "rotated" format (returning columns instead of rows)?

    - by Joshua Carmody
    Sorry for the lame title, my descriptive skills are poor today. In a nutshell, I have a query similar to the following: SELECT P.LAST_NAME, P.FIRST_NAME, D.DEMO_GROUP FROM PERSON P JOIN PERSON_DEMOGRAPHIC PD ON PD.PERSON_ID = P.PERSON_ID JOIN DEMOGRAPHIC D ON D.DEMOGRAPHIC_ID = PD.DEMOGRAPHIC_ID This returns output like this: LAST_NAME FIRST_NAME DEMO_GROUP --------------------------------------------- Johnson Bob Male Smith Jane Female Smith Jane Teacher Beeblebrox Zaphod Male Beeblebrox Zaphod Alien Beeblebrox Zaphid Politician I would prefer the output be similar to the following: LAST_NAME FIRST_NAME Male Female Teacher Alien Politician --------------------------------------------------------------------------------------------------------- Johnson Bob 1 0 0 0 0 Smith Jane 0 1 1 0 0 Beeblebrox Zaphod 1 0 0 1 1 The number of rows in the DEMOGRAPHIC table varies, so I can't say with certainty how many columns I need. The query needs to be flexible. Yes, it would be trivial to do this in code. But this query is one piece of a complicated set of stored procedures, views, and reporting services, many of which are outside my sphere of influence. I need to produce this output inside the database to avoid breaking the system. Any ideas? This is MS SQL Server 2005, by the way. Thanks.

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  • Sql serve Full Text Search with Containstable is very slow when Used in JOIN!

    - by Bob
    Hello, I am using sql 2008 full text search and I am having serious issues with performance depending on how I use Contains or ContainsTable. Here are sample: (table one has about 5000 records and there is a covered index on table1 which has all the fields in the where clause. I tried to simplify the statements so forgive me if there is syntax issues.) Scenario 1: select * from table1 as t1 where t1.field1=90 and t1.field2='something' and Exists(select top 1 * from containstable(table1,*, 'something') as t2 where t2.[key]=t1.id) results: 10 second (very slow) Scenario 2: select * from table1 as t1 join containstable(table1,*, 'something') as t2 on t2.[key] = t1.id where t1.field1=90 and t1.field2='something' results: 10 second (very slow) Scenario 3: Declare @tbl Table(id uniqueidentifier primary key) insert into @tbl select {key] from containstable(table1,*, 'something') select * from table1 as t1 where t1.field1=90 and t1.field2='something' and Exists(select id from @tbl as tbl where id=req1.id) results: fraction of a second (super fast) Bottom line, it seems if I use Containstable in any kind of join or where clause condition of a select statement that also has other conditions, the performance is really bad. In addition if you look at profiler, the number of reads from the database goes to the roof. But if I first do the full text search and put results in a table variable and use that variable everything goes super fast. The number of reads are also much lower. It seems in "bad" scenarios, somehow it gets stuck in a loop which causes it to read many times from teh database but of course I don't understant why. Now the question is first of all whyis that happening? and question two is that how scalable table variables are? what if it results to 10s of thousands of records? is it still going to be fast. Any ideas? Thanks

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  • Which DHT algorithm to use (if I want to join two separate DHTs)?

    - by webdreamer
    I've been looking into some DHT systems, specially Pastry and Chord. I've read some concerns about Chord's reaction to churn, though I believe that won't be a problem for the task I have at hands. I'm implementing some sort of social network service that doesn't rely on any central servers for a course project. I need the DHT for the lookups. Now I don't know of all the servers in the network in the beginning. As I've stated, there's no main tracker server. It works this way: each client has three dedicated servers. The three servers have the profile of the client, and it's wall, it's personal info, replicated. I only get to know about other group of servers when the user adds a friend (inputing the client's address). So I would create two separate DHTs on the two groups of three servers and when they friend each other I would like to join the DHTs. I would like to this consistently. I haven't had a lot of time to get all that familiar with the protocols, so I would like to know which one is better if I want to join the two separate DHTs?

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  • LINQ Join on Dictionary<K,T> where only K is changed.

    - by Stacey
    Assuming type TModel, TKey, and TValue. In a dictionary where KeyValuePair is declared, I need to merge TKey into a separate model of KeyValuePair where TKey in the original dictionary refers to an identifier in a list of TModel that will replace the item in the Dictionary. public TModel { public Guid Id { get; set; } // ... } public Dictionary<Guid, TValue> contains the elements. TValue relates to the TModel. The serialized/stored object is like this.. public SerializedModel { public Dictionary<Guid,TValue> Items { get; set; } } So I need to construct a new model... KeyValueModel { public Dictionary<TModel, TValue> { get; set; } } KeyValueModel kvm = = (from tModels in controller.ModelRepository.List<Models.Models>() join matchingModels in storedInformation.Items on tModels.Id equals matchingModels select tModels).ToDictionary( c => c.Id, storedInformation.Items.Values ) This linq query isn't doing what I'm wanting, but I think I'm at least headed in the right direction. Can anyone assist with the query? The original object is stored as a KeyValuePair. I need to merge the Guid Keys in the Dictionary to their actual related objects in another object (List) so that the final result is KeyValuePair. And as for what the query is not doing for me... it isn't compiling or running. It just says that "Join is not valid".

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  • Correlate GROUP BY and LEFT JOIN on multiple criteria to show latest record?

    - by Sunbird
    In a simple stock management database, quantity of new stock is added and shipped until quantity reaches zero. Each stock movement is assigned a reference, only the latest reference is used. In the example provided, the latest references are never shown, the stock ID's 1,4 should have references charlie, foxtrot respectively, but instead show alpha, delta. How can a GROUP BY and LEFT JOIN on multiple criteria be correlated to show the latest record? http://sqlfiddle.com/#!2/6bf37/107 CREATE TABLE stock ( id tinyint PRIMARY KEY, quantity int, parent_id tinyint ); CREATE TABLE stock_reference ( id tinyint PRIMARY KEY, stock_id tinyint, stock_reference_type_id tinyint, reference varchar(50) ); CREATE TABLE stock_reference_type ( id tinyint PRIMARY KEY, name varchar(50) ); INSERT INTO stock VALUES (1, 10, 1), (2, -5, 1), (3, -5, 1), (4, 20, 4), (5, -10, 4), (6, -5, 4); INSERT INTO stock_reference VALUES (1, 1, 1, 'Alpha'), (2, 2, 1, 'Beta'), (3, 3, 1, 'Charlie'), (4, 4, 1, 'Delta'), (5, 5, 1, 'Echo'), (6, 6, 1, 'Foxtrot'); INSERT INTO stock_reference_type VALUES (1, 'Customer Reference'); SELECT stock.id, SUM(stock.quantity) as quantity, customer.reference FROM stock LEFT JOIN stock_reference AS customer ON stock.id = customer.stock_id AND stock_reference_type_id = 1 GROUP BY stock.parent_id

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  • How To Join Tables from Two Different Contexts with LINQ2SQL?

    - by RSolberg
    I have 2 data contexts in my application (different databases) and need to be able to query a table in context A with a right join on a table in context B. How do I go about doing this in LINQ2SQL? Why?: We are using a SaaS product for tracking our time, projects, etc. and would like to send new service requests to this product to prevent our team from duplicating data entry. Context A: This db stores service request information. It is a third party DB and we are not able to make changes to the structure of this DB as it could have unintended non-supportable consequences downstream. Context B: This data stores the "log" data of service requests that have been processed. My team and I have full control over this DB's structure, etc. Unprocessed service requests should find their way into this DB and another process will identify it as not being processed and send the record to the SaaS product. This is the query that I am looking to modify. I was able to do a !list.Contains(c.swHDCaseId) initially, but this cannot handle more than 2100 items. Is there a way to add a join to the other context? var query = (from c in contextA.Cases where monitoredInboxList.Contains(c.INBOXES.inboxName) select new { //setup fields here... });

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  • Most efficient way to LIMIT results in a JOIN?

    - by johnnietheblack
    I have a fairly simple one-to-many type join in a MySQL query. In this case, I'd like to LIMIT my results by the left table. For example, let's say I have an accounts table and a comments table, and I'd like to pull 100 rows from accounts and all the associated comments rows for each. Thy only way I can think to do this is with a sub-select in in the FROM clause instead of simply selecting FROM accounts. Here is my current idea: SELECT a.*, c.* FROM (SELECT * FROM accounts LIMIT 100) a LEFT JOIN `comments` c on c.account_id = a.id ORDER BY a.id However, whenever I need to do a sub-select of some sort, my intermediate level SQL knowledge feels like it's doing something wrong. Is there a more efficient, or faster, way to do this, or is this pretty good? By the way... This might be the absolute simplest way to do this, which I'm okay with as an answer. I'm simply trying to figure out if there IS another way to do this that could potentially compete with the above statement in terms of speed.

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  • whats wrong in this LINQ synatx?

    - by Saurabh Kumar
    Hi, I am trying to convert a SQL query to LINQ. Somehow my count(distinct(x)) logic does not seem to be working correctly. The original SQL is quite efficient(or so i think), but the generated SQL is not even returning the correct result. I am trying to fix this LINQ to do what the original SQL is doing, AND in an efficient way as the original query is doing. Help here would be really apreciated as I am stuck here :( SQL which is working and I need to make a comparable LINQ of: SELECT [t1].[PersonID] AS [personid] FROM [dbo].[Code] AS [t0] INNER JOIN [dbo].[phonenumbers] AS [t1] ON [t1].[PhoneCode] = [t0].[Code] INNER JOIN [dbo].[person] ON [t1].[PersonID]= [dbo].[Person].PersonID WHERE ([t0].[codetype] = 'phone') AND ( ([t0].[CodeDescription] = 'Home') AND ([t1].[PhoneNum] = '111') OR ([t0].[CodeDescription] = 'Work') AND ([t1].[PhoneNum] = '222') ) GROUP BY [t1].[PersonID] HAVING COUNT(DISTINCT([t1].[PhoneNum]))=2 The LINQ which I made is approximately as below: var ids = context.Code.Where(predicate); var rs = from r in ids group r by new { r.phonenumbers.person.PersonID} into g let matchcount=g.Select(p => p.phonenumbers.PhoneNum).Distinct().Count() where matchcount ==2 select new { personid = g.Key }; Unfortunately, the above LINQ is NOT generating the correct result, and is actually internally getting generated to the SQL shown below. By the way, this generated query is also reading ALL the rows(about 19592040) around 2 times due to the COUNTS :( Wich is a big performance issue too. Please help/point me to the right direction. Declare @p0 VarChar(10)='phone' Declare @p1 VarChar(10)='Home' Declare @p2 VarChar(10)='111' Declare @p3 VarChar(10)='Work' Declare @p4 VarChar(10)='222' Declare @p5 VarChar(10)='2' SELECT [t9].[PersonID], ( SELECT COUNT(*) FROM ( SELECT DISTINCT [t13].[PhoneNum] FROM [dbo].[Code] AS [t10] INNER JOIN [dbo].[phonenumbers] AS [t11] ON [t11].[PhoneType] = [t10].[Code] INNER JOIN [dbo].[Person] AS [t12] ON [t12].[PersonID] = [t11].[PersonID] INNER JOIN [dbo].[phonenumbers] AS [t13] ON [t13].[PhoneType] = [t10].[Code] WHERE ([t9].[PersonID] = [t12].[PersonID]) AND ([t10].[codetype] = @p0) AND ((([t10].[codetype] = @p1) AND ([t11].[PhoneNum] = @p2)) OR (([t10].[codetype] = @p3) AND ([t11].[PhoneNum] = @p4))) ) AS [t14] ) AS [cnt] FROM ( SELECT [t3].[PersonID], ( SELECT COUNT(*) FROM ( SELECT DISTINCT [t7].[PhoneNum] FROM [dbo].[Code] AS [t4] INNER JOIN [dbo].[phonenumbers] AS [t5] ON [t5].[PhoneType] = [t4].[Code] INNER JOIN [dbo].[Person] AS [t6] ON [t6].[PersonID] = [t5].[PersonID] INNER JOIN [dbo].[phonenumbers] AS [t7] ON [t7].[PhoneType] = [t4].[Code] WHERE ([t3].[PersonID] = [t6].[PersonID]) AND ([t4].[codetype] = @p0) AND ((([t4].[codetype] = @p1) AND ([t5].[PhoneNum] = @p2)) OR (([t4].[codetype] = @p3) AND ([t5].[PhoneNum] = @p4))) ) AS [t8] ) AS [value] FROM ( SELECT [t2].[PersonID] FROM [dbo].[Code] AS [t0] INNER JOIN [dbo].[phonenumbers] AS [t1] ON [t1].[PhoneType] = [t0].[Code] INNER JOIN [dbo].[Person] AS [t2] ON [t2].[PersonID] = [t1].[PersonID] WHERE ([t0].[codetype] = @p0) AND ((([t0].[codetype] = @p1) AND ([t1].[PhoneNum] = @p2)) OR (([t0].[codetype] = @p3) AND ([t1].[PhoneNum] = @p4))) GROUP BY [t2].[PersonID] ) AS [t3] ) AS [t9] WHERE [t9].[value] = @p5 Thanks!

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  • Optimize MySQL query (ngrams, COUNT(), GROUP BY, ORDER BY)

    - by Gerardo
    I have a database with thousands of companies and their locations. I have implemented n-grams to optimize search. I am making one query to retrieve all the companies that match with the search query and another one to get a list with their locations and the number of companies in each location. The query I am trying to optimize is the latter. Maybe the problem is this: Every company ('anunciante') has a field ('estado') to make logical deletes. So, if 'estado' equals 1, the company should be retrieved. When I run the EXPLAIN command, it shows that it goes through almost 40k rows, when the actual result (the reality matching companies) are 80. How can I optimize this? This is my query (XXX represent the n-grams for the search query): SELECT provincias.provincia AS provincia, provincias.id, COUNT(*) AS cantidad FROM anunciantes JOIN anunciante_invertido AS a_i0 ON anunciantes.id = a_i0.id_anunciante JOIN indice_invertido AS indice0 ON a_i0.id_invertido = indice0.id LEFT OUTER JOIN domicilios ON anunciantes.id = domicilios.id_anunciante LEFT OUTER JOIN localidades ON domicilios.id_localidad = localidades.id LEFT OUTER JOIN provincias ON provincias.id = localidades.id_provincia WHERE anunciantes.estado = 1 AND indice0.id IN (SELECT invertido_ngrama.id_palabra FROM invertido_ngrama JOIN ngrama ON ngrama.id = invertido_ngrama.id_ngrama WHERE ngrama.ngrama = 'XXX') AND indice0.id IN (SELECT invertido_ngrama.id_palabra FROM invertido_ngrama JOIN ngrama ON ngrama.id = invertido_ngrama.id_ngrama WHERE ngrama.ngrama = 'XXX') AND indice0.id IN (SELECT invertido_ngrama.id_palabra FROM invertido_ngrama JOIN ngrama ON ngrama.id = invertido_ngrama.id_ngrama WHERE ngrama.ngrama = 'XXX') AND indice0.id IN (SELECT invertido_ngrama.id_palabra FROM invertido_ngrama JOIN ngrama ON ngrama.id = invertido_ngrama.id_ngrama WHERE ngrama.ngrama = 'XXX') AND indice0.id IN (SELECT invertido_ngrama.id_palabra FROM invertido_ngrama JOIN ngrama ON ngrama.id = invertido_ngrama.id_ngrama WHERE ngrama.ngrama = 'XXX') GROUP BY provincias.id ORDER BY cantidad DESC And this is the query explained (hope it can be read in this format): id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY anunciantes ref PRIMARY,estado estado 1 const 36669 Using index; Using temporary; Using filesort 1 PRIMARY domicilios ref id_anunciante id_anunciante 4 db84771_viaempresas.anunciantes.id 1 1 PRIMARY localidades eq_ref PRIMARY PRIMARY 4 db84771_viaempresas.domicilios.id_localidad 1 1 PRIMARY provincias eq_ref PRIMARY PRIMARY 4 db84771_viaempresas.localidades.id_provincia 1 1 PRIMARY a_i0 ref PRIMARY,id_anunciante,id_invertido PRIMARY 4 db84771_viaempresas.anunciantes.id 1 Using where; Using index 1 PRIMARY indice0 eq_ref PRIMARY PRIMARY 4 db84771_viaempresas.a_i0.id_invertido 1 Using index 6 DEPENDENT SUBQUERY ngrama const PRIMARY,ngrama ngrama 5 const 1 Using index 6 DEPENDENT SUBQUERY invertido_ngrama eq_ref PRIMARY,id_palabra,id_ngrama PRIMARY 8 func,const 1 Using index 5 DEPENDENT SUBQUERY ngrama const PRIMARY,ngrama ngrama 5 const 1 Using index 5 DEPENDENT SUBQUERY invertido_ngrama eq_ref PRIMARY,id_palabra,id_ngrama PRIMARY 8 func,const 1 Using index 4 DEPENDENT SUBQUERY ngrama const PRIMARY,ngrama ngrama 5 const 1 Using index 4 DEPENDENT SUBQUERY invertido_ngrama eq_ref PRIMARY,id_palabra,id_ngrama PRIMARY 8 func,const 1 Using index 3 DEPENDENT SUBQUERY ngrama const PRIMARY,ngrama ngrama 5 const 1 Using index 3 DEPENDENT SUBQUERY invertido_ngrama eq_ref PRIMARY,id_palabra,id_ngrama PRIMARY 8 func,const 1 Using index 2 DEPENDENT SUBQUERY ngrama const PRIMARY,ngrama ngrama 5 const 1 Using index 2 DEPENDENT SUBQUERY invertido_ngrama eq_ref PRIMARY,id_palabra,id_ngrama PRIMARY 8 func,const 1 Using index

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  • How to select all parent objects into DataContext using single LINQ query ?

    - by too
    I am looking for an answer to a specific problem of fetching whole LINQ object hierarchy using single SELECT. At first I was trying to fill as much LINQ objects as possible using LoadOptions, but AFAIK this method allows only single table to be linked in one query using LoadWith. So I have invented a solution to forcibly set all parent objects of entity which of list is to be fetched, although there is a problem of multiple SELECTS going to database - a single query results in two SELECTS with the same parameters in the same LINQ context. For this question I have simplified this query to popular invoice example: public static class Extensions { public static IEnumerable<T> ForEach<T>(this IEnumerable<T> collection, Action<T> func) { foreach(var c in collection) { func(c); } return collection; } } public IEnumerable<Entry> GetResults(AppDataContext context, int CustomerId) { return ( from entry in context.Entries join invoice in context.Invoices on entry.EntryInvoiceId equals invoice.InvoiceId join period in context.Periods on invoice.InvoicePeriodId equals period.PeriodId // LEFT OUTER JOIN, store is not mandatory join store in context.Stores on entry.EntryStoreId equals store.StoreId into condStore from store in condStore.DefaultIfEmpty() where (invoice.InvoiceCustomerId = CustomerId) orderby entry.EntryPrice descending select new { Entry = entry, Invoice = invoice, Period = period, Store = store } ).ForEach(x => { x.Entry.Invoice = Invoice; x.Invoice.Period = Period; x.Entry.Store = Store; } ).Select(x => x.Entry); } When calling this function and traversing through result set, for example: var entries = GetResults(this.Context); int withoutStore = 0; foreach(var k in entries) { if(k.EntryStoreId == null) withoutStore++; } the resulting query to database looks like (single result is fetched): SELECT [t0].[EntryId], [t0].[EntryInvoiceId], [t0].[EntryStoreId], [t0].[EntryProductId], [t0].[EntryQuantity], [t0].[EntryPrice], [t1].[InvoiceId], [t1].[InvoiceCustomerId], [t1].[InvoiceDate], [t1].[InvoicePeriodId], [t2].[PeriodId], [t2].[PeriodName], [t2].[PeriodDateFrom], [t4].[StoreId], [t4].[StoreName] FROM [Entry] AS [t0] INNER JOIN [Invoice] AS [t1] ON [t0].[EntryInvoiceId] = [t1].[InvoiceId] INNER JOIN [Period] AS [t2] ON [t2].[PeriodId] = [t1].[InvoicePeriodId] LEFT OUTER JOIN ( SELECT 1 AS [test], [t3].[StoreId], [t3].[StoreName] FROM [Store] AS [t3] ) AS [t4] ON [t4].[StoreId] = ([t0].[EntryStoreId]) WHERE (([t1].[InvoiceCustomerId]) = @p0) ORDER BY [t0].[InvoicePrice] DESC -- @p0: Input Int (Size = 0; Prec = 0; Scale = 0) [186] -- Context: SqlProvider(Sql2008) Model: AttributedMetaModel Build: 3.5.30729.1 SELECT [t0].[EntryId], [t0].[EntryInvoiceId], [t0].[EntryStoreId], [t0].[EntryProductId], [t0].[EntryQuantity], [t0].[EntryPrice], [t1].[InvoiceId], [t1].[InvoiceCustomerId], [t1].[InvoiceDate], [t1].[InvoicePeriodId], [t2].[PeriodId], [t2].[PeriodName], [t2].[PeriodDateFrom], [t4].[StoreId], [t4].[StoreName] FROM [Entry] AS [t0] INNER JOIN [Invoice] AS [t1] ON [t0].[EntryInvoiceId] = [t1].[InvoiceId] INNER JOIN [Period] AS [t2] ON [t2].[PeriodId] = [t1].[InvoicePeriodId] LEFT OUTER JOIN ( SELECT 1 AS [test], [t3].[StoreId], [t3].[StoreName] FROM [Store] AS [t3] ) AS [t4] ON [t4].[StoreId] = ([t0].[EntryStoreId]) WHERE (([t1].[InvoiceCustomerId]) = @p0) ORDER BY [t0].[InvoicePrice] DESC -- @p0: Input Int (Size = 0; Prec = 0; Scale = 0) [186] -- Context: SqlProvider(Sql2008) Model: AttributedMetaModel Build: 3.5.30729.1 The question is why there are two queries and how can I fetch LINQ objects without such hacks?

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  • LINQ nested joins

    - by ace
    Im trying to convert a SQL join to LINQ. I need some help in getting the nested join working in LINQ. This is my SQL query, Ive cut it short just to show the nested join in SQL: LEFT OUTER JOIN dbo.TaskCommentRecipient RIGHT OUTER JOIN dbo.TaskComment ON dbo.TaskCommentRecipient.TaskCommentID = dbo.TaskComment.TaskCommentID ON dbo.Task.Taskid = dbo.TaskComment.TaskCommentTaskId

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  • Working with Joins in LINQ

    - by vik20000in
    While working with data most of the time we have to work with relation between different lists of data. Many a times we want to fetch data from both the list at once. This requires us to make different kind of joins between the lists of data. LINQ support different kinds of join Inner Join     List<Customer> customers = GetCustomerList();     List<Supplier> suppliers = GetSupplierList();      var custSupJoin =         from sup in suppliers         join cust in customers on sup.Country equals cust.Country         select new { Country = sup.Country, SupplierName = sup.SupplierName, CustomerName = cust.CompanyName }; Group Join – where By the joined dataset is also grouped.     List<Customer> customers = GetCustomerList();     List<Supplier> suppliers = GetSupplierList();      var custSupQuery =         from sup in suppliers         join cust in customers on sup.Country equals cust.Country into cs         select new { Key = sup.Country, Items = cs }; We can also work with the Left outer join in LINQ like this.     List<Customer> customers = GetCustomerList();     List<Supplier> suppliers = GetSupplierList();      var supplierCusts =         from sup in suppliers         join cust in customers on sup.Country equals cust.Country into cs         from c in cs.DefaultIfEmpty()  // DefaultIfEmpty preserves left-hand elements that have no matches on the right side         orderby sup.SupplierName         select new { Country = sup.Country, CompanyName = c == null ? "(No customers)" : c.CompanyName,                      SupplierName = sup.SupplierName};Vikram

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  • Oracle????????????????????????~????????????????????

    - by Yusuke.Yamamoto
    RDBMS ???????·????????????????????????????????????????????????????????????????????????? ????????Oracle ?????????????????????????????????? Oracle Database ???????????????????????????????? ????????????????????? ????Oracle???????????????????????????????????????????????????????????????????????????? ?????????????? Oracle Database ???????????????????????? ??????????????????????????????????2????????????? 1. ??????(Query Transformation) Query Transformation ???????SQL??????????????????SQL????????????????????? Query Transformation ???Predicate Transformation ? Common Sub-expression Elimination (CSE), Order-BY Elimination (OBYE), Outer Join Elimination (OJE), Simple View Meging (SVM), Predicate Move around (PM), Complex View Merging (CVM), Sub-query Unnesting (SU), Join Predicate Push Down (JPPD) ???? OR Expansion, Star Transformation (ST) ????????????? ···???????????????????????????????????????????????????? Predicate Transformation ?????? Transitive Predicate Generation ????????????? ?????????????SQL???deptno ? 10 ????????????????????????????? select e.ename, d.loc from emp e, dept d where e.deptno=d.deptno and e.deptno=10; ???????????????emp ??? deptno=10 ??????????????dept ??? d.deptno=10 ??????????????????? emp ?? deptno=10 ????????????????????emp ?? deptno=10 ??????10???????10? dept ????????????dept ??20???????????????????????10?*20?=200?????(??????????·?????????)? ??SQL?? Transitive Predicate Generation ??????SQL????????????????? select e.ename, d.location from emp e, dept d where e.deptno=d.deptno and e.deptno=10 and d.deptno=10; ^^^^^^^^^^^ ??????dept ?????? deptno=10 ??????????????????????????10?*1?=10(dept.deptno ?unique????)?1/20????????????????1/20????????????????10??????????30???????????????Query Transformation ???????????????????????????? ?:??????????? dept ?? 1-row table ??????dept ?? driving ???(Outer Table)??? emp ?? probe ???(Inner Table)????????????1?*10?=10 ????????????????????????????????????????????????????????1/20????????????? ?????? Query Transformation ??????SQL????????????????????????????????? Transformation ??????????????????????????????????? 2. ????·????(Access Path Analysis) Access Path Analysis ??Query Transformation ??SQL????????????(Access Path)?????????(Join Method)?????(Join Order)?????????? ??????????????????(FTS)?ROWID?????????????????????????????·?????(Nested Loop Join)???????(Hash Join)????/?????(Sort Merge Join)????????????????????????????????????????????????????????????????????????? Oracle Database ????????? Query Transformation ???? Logical Optimizer?Access Path Analysis ???? Physical Optimizer ????????? ??????????????????????????????????????????????????????????????????????????????????????????????????? ????????????????????????????????????????????????????? Oracle Database ????????????????????? "Oracle ????????" ?????????? Sustaining Engineering?? ?(??? ???) ???????????????? Sustaining Engineering ????????????????????????Oracle Database ???????????????????????? ?????????????????????Ruby????????????????????????? Oracle????????????????????????! Oracle????????????? Oracle????????????????????????

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  • How to use join in EntityQuery,.. using RIA and Entities

    - by mian
    Hi i use the following patterh for fetching data using RIA objTestAppContext is an instance of LinqToEntitiesDomainService class EntityQuery query = from tmpTable in objTestAppContext.GteOrdrs() where tmpTable.orderID == d select tmpTable; Now scenerio is ,, that I also have a OrderDetail entity in EDMS which is attached to he Order as orderID in OrderDetails which is managed by the association set named as FK_orderdetals_orders. Please tell how can i use join in the "query"

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  • How to do a join of 3 files with awk by first Column?

    - by noinflection
    i have three similar files, they are all like this: ID1 Value1a ID2 Value2a . . . IDN Value2n and i want an output like this ID1 Value1a Value1b Value1c ID2 Value2a Value2b Value2c ..... IDN ValueNa ValueNb ValueNc Looking to the first line i want value1A to be the value of id1 in fileA, value1B the value of id1 in fileB, etc, i think of it like a nice sql join. I've tried several things but none of them where even close.

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  • What are the benefits of left outer join vs nested aggregate selects to find the newest rows in a table?

    - by RenderIn
    I'm doing: select * from mytable y where y.year = (select max(yi.year) from mytable yi where yi.person = y.person) Is that better or worse from a performance aspect than: select y.* from mytable y left outer join mytable y2 on y.year < y2.year and y.person = y2.person where y2.year is null The explain plan/anecdotal evidence is inconclusive so I am wondering if in general one is better than the other.

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  • join same rails models twice, eg people has_many clubs through membership AND people has_many clubs through committee

    - by Ben
    Models: * Person * Club Relationships * Membership * Committee People should be able to join a club (Membership) People should be able to be on the board of a club (Committee) For my application these involve vastly different features, so I would prefer not to use a flag to set (is_board_member) or similar. I find myself wanting to write: People has_many :clubs :through = :membership # :as = :member? :foreign_key = :member_id? has_many :clubs :through = :committee # as (above) but I'm not really sure how to stitch this together

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