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• Big Data – Data Mining with Hive – What is Hive? – What is HiveQL (HQL)? – Day 15 of 21

  - by Pinal Dave

  In yesterday’s blog post we learned the importance of the operational database in Big Data Story. In this article we will understand what is Hive and HQL in Big Data Story. Yahoo started working on PIG (we will understand that in the next blog post) for their application deployment on Hadoop. The goal of Yahoo to manage their unstructured data. Similarly Facebook started deploying their warehouse solutions on Hadoop which has resulted in HIVE. The reason for going with HIVE is because the traditional warehousing solutions are getting very expensive. What is HIVE? Hive is a datawarehouseing infrastructure for Hadoop. The primary responsibility is to provide data summarization, query and analysis. It  supports analysis of large datasets stored in Hadoop’s HDFS as well as on the Amazon S3 filesystem. The best part of HIVE is that it supports SQL-Like access to structured data which is known as HiveQL (or HQL) as well as big data analysis with the help of MapReduce. Hive is not built to get a quick response to queries but it it is built for data mining applications. Data mining applications can take from several minutes to several hours to analysis the data and HIVE is primarily used there. HIVE Organization The data are organized in three different formats in HIVE. Tables: They are very similar to RDBMS tables and contains rows and tables. Hive is just layered over the Hadoop File System (HDFS), hence tables are directly mapped to directories of the filesystems. It also supports tables stored in other native file systems. Partitions: Hive tables can have more than one partition. They are mapped to subdirectories and file systems as well. Buckets: In Hive data may be divided into buckets. Buckets are stored as files in partition in the underlying file system. Hive also has metastore which stores all the metadata. It is a relational database containing various information related to Hive Schema (column types, owners, key-value data, statistics etc.). We can use MySQL database over here. What is HiveSQL (HQL)? Hive query language provides the basic SQL like operations. Here are few of the tasks which HQL can do easily. Create and manage tables and partitions Support various Relational, Arithmetic and Logical Operators Evaluate functions Download the contents of a table to a local directory or result of queries to HDFS directory Here is the example of the HQL Query: SELECT upper(name), salesprice FROM sales; SELECT category, count(1) FROM products GROUP BY category; When you look at the above query, you can see they are very similar to SQL like queries. Tomorrow In tomorrow’s blog post we will discuss about very important components of the Big Data Ecosystem – Pig. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Big Data, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL

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• SQL SERVER – UNION ALL and ORDER BY – How to Order Table Separately While Using UNION ALL

  - by pinaldave

  I often see developers trying following syntax while using ORDER BY. SELECT Columns FROM TABLE1 ORDER BY Columns UNION ALL SELECT Columns FROM TABLE2 ORDER BY Columns However the above query will return following error. Msg 156, Level 15, State 1, Line 5 Incorrect syntax near the keyword ‘ORDER’. It is not possible to use two different ORDER BY in the UNION statement. UNION returns single resultsetand as per the Logical Query Processing Phases. However, if your requirement is such that you want your top and bottom query of the UNION resultset independently sorted but in the same resultset you can add an additional static column and order by that column. Let us re-create the same scenario. First create two tables and populated with sample data. USE tempdb GO -- Create table CREATE TABLE t1 (ID INT, Col1 VARCHAR(100)); CREATE TABLE t2 (ID INT, Col1 VARCHAR(100)); GO -- Sample Data Build INSERT INTO t1 (ID, Col1) SELECT 1, 'Col1-t1' UNION ALL SELECT 2, 'Col2-t1' UNION ALL SELECT 3, 'Col3-t1'; INSERT INTO t2 (ID, Col1) SELECT 3, 'Col1-t2' UNION ALL SELECT 2, 'Col2-t2' UNION ALL SELECT 1, 'Col3-t2'; GO If we SELECT the data from both the table using UNION ALL . -- SELECT without ORDER BY SELECT ID, Col1 FROM t1 UNION ALL SELECT ID, Col1 FROM t2 GO We will get the data in following order. However, our requirement is to get data in following order. If we need data ordered by Column1 we can ORDER the resultset ordered by Column1. -- SELECT with ORDER BY SELECT ID, Col1 FROM t1 UNION ALL SELECT ID, Col1 FROM t2 ORDER BY ID GO Now to get the data in independently sorted in UNION ALL let us add additional column OrderKey and use ORDER BY  on that column. I think the description does not do proper justice let us see the example here. -- SELECT with ORDER BY - with ORDER KEY SELECT ID, Col1, 'id1' OrderKey FROM t1 UNION ALL SELECT ID, Col1, 'id2' OrderKey FROM t2 ORDER BY OrderKey, ID GO The above query will give the desired result. Now do not forget to clean up the database by running the following script. -- Clean up DROP TABLE t1; DROP TABLE t2; GO Here is the complete script used in this example. USE tempdb GO -- Create table CREATE TABLE t1 (ID INT, Col1 VARCHAR(100)); CREATE TABLE t2 (ID INT, Col1 VARCHAR(100)); GO -- Sample Data Build INSERT INTO t1 (ID, Col1) SELECT 1, 'Col1-t1' UNION ALL SELECT 2, 'Col2-t1' UNION ALL SELECT 3, 'Col3-t1'; INSERT INTO t2 (ID, Col1) SELECT 3, 'Col1-t2' UNION ALL SELECT 2, 'Col2-t2' UNION ALL SELECT 1, 'Col3-t2'; GO -- SELECT without ORDER BY SELECT ID, Col1 FROM t1 UNION ALL SELECT ID, Col1 FROM t2 GO -- SELECT with ORDER BY SELECT ID, Col1 FROM t1 UNION ALL SELECT ID, Col1 FROM t2 ORDER BY ID GO -- SELECT with ORDER BY - with ORDER KEY SELECT ID, Col1, 'id1' OrderKey FROM t1 UNION ALL SELECT ID, Col1, 'id2' OrderKey FROM t2 ORDER BY OrderKey, ID GO -- Clean up DROP TABLE t1; DROP TABLE t2; GO I am sure there are many more ways to achieve this, what method would you use if you have to face the similar situation? Reference: Pinal Dave (http://blog.sqlauthority.com)   Filed under: Best Practices, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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• SQL SERVER – Select Columns from Stored Procedure Resultset

  - by Pinal Dave

  It is fun to go back to basics often. Here is the one classic question: “How to select columns from Stored Procedure Resultset?” Though Stored Procedure has been introduced many years ago, the question about retrieving columns from Stored Procedure is still very popular with beginners. Let us see the solution in quick steps. First we will create a sample stored procedure. CREATE PROCEDURE SampleSP AS SELECT 1 AS Col1, 2 AS Col2 UNION SELECT 11, 22 GO Now we will create a table where we will temporarily store the result set of stored procedures. We will be using INSERT INTO and EXEC command to retrieve the values and insert into temporary table. CREATE TABLE #TempTable (Col1 INT, Col2 INT) GO INSERT INTO #TempTable EXEC SampleSP GO Next we will retrieve our data from stored procedure. SELECT * FROM #TempTable GO Finally we will clean up all the objects which we have created. DROP TABLE #TempTable DROP PROCEDURE SampleSP GO Let me know if you want me to share such back to basic tips. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Stored Procedure, SQL Tips and Tricks, T SQL

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• Whether to use UNION or OR in SQL Server Queries

  - by Dinesh Asanka

  Recently I came across with an article on DB2 about using Union instead of OR. So I thought of carrying out a research on SQL Server on what scenarios UNION is optimal in and which scenarios OR would be best. I will analyze this with a few scenarios using samples taken  from the AdventureWorks database Sales.SalesOrderDetail table. Scenario 1: Selecting all columns So we are going to select all columns and you have a non-clustered index on the ProductID column. --Query 1 : OR SELECT * FROM Sales.SalesOrderDetail WHERE ProductID = 714 OR ProductID =709 OR ProductID =998 OR ProductID =875 OR ProductID =976 OR ProductID =874 --Query 2 : UNION SELECT * FROM Sales.SalesOrderDetail WHERE ProductID = 714 UNION SELECT * FROM Sales.SalesOrderDetail WHERE ProductID = 709 UNION SELECT * FROM Sales.SalesOrderDetail WHERE ProductID = 998 UNION SELECT * FROM Sales.SalesOrderDetail WHERE ProductID = 875 UNION SELECT * FROM Sales.SalesOrderDetail WHERE ProductID = 976 UNION SELECT * FROM Sales.SalesOrderDetail WHERE ProductID = 874 So query 1 is using OR and the later is using UNION. Let us analyze the execution plans for these queries. Query 1 Query 2 As expected Query 1 will use Clustered Index Scan but Query 2, uses all sorts of things. In this case, since it is using multiple CPUs you might have CX_PACKET waits as well. Let’s look at the profiler results for these two queries: CPU Reads Duration Row Counts OR 78 1252 389 3854 UNION 250 7495 660 3854 You can see from the above table the UNION query is not performing well as the  OR query though both are retuning same no of rows (3854).These results indicate that, for the above scenario UNION should be used. Scenario 2: Non-Clustered and Clustered Index Columns only --Query 1 : OR SELECT ProductID,SalesOrderID, SalesOrderDetailID FROM Sales.SalesOrderDetail WHERE ProductID = 714 OR ProductID =709 OR ProductID =998 OR ProductID =875 OR ProductID =976 OR ProductID =874 GO --Query 2 : UNION SELECT ProductID,SalesOrderID, SalesOrderDetailID FROM Sales.SalesOrderDetail WHERE ProductID = 714 UNION SELECT ProductID,SalesOrderID, SalesOrderDetailID FROM Sales.SalesOrderDetail WHERE ProductID = 709 UNION SELECT ProductID,SalesOrderID, SalesOrderDetailID FROM Sales.SalesOrderDetail WHERE ProductID = 998 UNION SELECT ProductID,SalesOrderID, SalesOrderDetailID FROM Sales.SalesOrderDetail WHERE ProductID = 875 UNION SELECT ProductID,SalesOrderID, SalesOrderDetailID FROM Sales.SalesOrderDetail WHERE ProductID = 976 UNION SELECT ProductID,SalesOrderID, SalesOrderDetailID FROM Sales.SalesOrderDetail WHERE ProductID = 874 GO So this time, we will be selecting only index columns, which means these queries will avoid a data page lookup. As in the previous case we will analyze the execution plans: Query 1 Query 2 Again, Query 2 is more complex than Query 1. Let us look at the profile analysis: CPU Reads Duration Row Counts OR 0 24 208 3854 UNION 0 38 193 3854 In this analyzis, there is only slight difference between OR and UNION. Scenario 3: Selecting all columns for different fields Up to now, we were using only one column (ProductID) in the where clause.  What if we have two columns for where clauses and let us assume both are covered by non-clustered indexes? --Query 1 : OR SELECT * FROM Sales.SalesOrderDetail WHERE ProductID = 714 OR CarrierTrackingNumber LIKE 'D0B8%' --Query 2 : UNION SELECT * FROM Sales.SalesOrderDetail WHERE ProductID = 714 UNION SELECT * FROM Sales.SalesOrderDetail WHERE CarrierTrackingNumber  LIKE 'D0B8%' Query 1 Query 2: As we can see, the query plan for the second query has improved. Let us see the profiler results. CPU Reads Duration Row Counts OR 47 1278 443 1228 UNION 31 1334 400 1228 So in this case too, there is little difference between OR and UNION. Scenario 4: Selecting Clustered index columns for different fields Now let us go only with clustered indexes: --Query 1 : OR SELECT * FROM Sales.SalesOrderDetail WHERE ProductID = 714 OR CarrierTrackingNumber LIKE 'D0B8%' --Query 2 : UNION SELECT * FROM Sales.SalesOrderDetail WHERE ProductID = 714 UNION SELECT * FROM Sales.SalesOrderDetail WHERE CarrierTrackingNumber  LIKE 'D0B8%' Query 1 Query 2 Now both execution plans are almost identical except is an additional Stream Aggregate is used in the first query. This means UNION has advantage over OR in this scenario. Let us see profiler results for these queries again. CPU Reads Duration Row Counts OR 0 319 366 1228 UNION 0 50 193 1228 Now see the differences, in this scenario UNION has somewhat of an advantage over OR. Conclusion Using UNION or OR depends on the scenario you are faced with. So you need to do your analyzing before selecting the appropriate method. Also, above the four scenarios are not all an exhaustive list of scenarios, I selected those for the broad description purposes only.

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• SQL SERVER – Get Directory Structure using Extended Stored Procedure xp_dirtree

  - by pinaldave

  Many years ago I wrote article SQL SERVER – Get a List of Fixed Hard Drive and Free Space on Server where I demonstrated using undocumented Stored Procedure to find the drive letter in local system and available free space. I received question in email from reader asking if there any way he can list directory structure within the T-SQL. When I inquired more he suggested that he needs this because he wanted set up backup of the data in certain structure. Well, there is one undocumented stored procedure exists which can do the same. However, please be vary to use any undocumented procedures. xp_dirtree 'C:\Windows' Execution of the above stored procedure will give following result. If you prefer you can insert the data in the temptable and use the same for further use. Here is the quick script which will insert the data into the temptable and retrieve from the same. CREATE TABLE #TempTable (Subdirectory VARCHAR(512), Depth INT); INSERT INTO #TempTable (Subdirectory, Depth) EXEC xp_dirtree 'C:\Windows' SELECT Subdirectory, Depth FROM #TempTable; DROP TABLE #TempTable; Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Stored Procedure, SQL Tips and Tricks, SQLServer, T SQL, Technology

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• SQL SERVER – Puzzle to Win Print Book – Functions FIRST_VALUE and LAST_VALUE with OVER clause and ORDER BY

  - by pinaldave

  Some time an interesting feature and smart audience makes total difference at places. From last two days, I have been writing on SQL Server 2012 feature FIRST_VALUE and LAST_VALUE. Please read following post before I continue today as this question is based on the same. Introduction to FIRST_VALUE and LAST_VALUE Introduction to FIRST_VALUE and LAST_VALUE with OVER clause As a comment of the second post I received excellent question from Nilesh Molankar. He asks what will happen if we change few things in the T-SQL. I really like this question as this kind of questions will make us sharp and help us perform in critical situation in need. We recently publish SQL Server Interview Questions book. I promise that in future version of this book, we will for sure include this question. Instead of repeating his question, I am going to ask something very similar to his question. Let us first run following query (read yesterday’s blog post for more detail): USE AdventureWorks GO SELECT s.SalesOrderID,s.SalesOrderDetailID,s.OrderQty, FIRST_VALUE(SalesOrderDetailID) OVER (PARTITION BY SalesOrderID ORDER BY SalesOrderDetailID ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) FstValue, LAST_VALUE(SalesOrderDetailID) OVER (PARTITION BY SalesOrderID ORDER BY SalesOrderDetailID ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) LstValue FROM Sales.SalesOrderDetail s WHERE SalesOrderID IN (43670, 43669, 43667, 43663) ORDER BY s.SalesOrderID,s.SalesOrderDetailID,s.OrderQty GO Here is the resultset of the above query. Now let us change the ORDER BY clause of OVER clause in above query and see what is the new result. USE AdventureWorks GO SELECT s.SalesOrderID,s.SalesOrderDetailID,s.OrderQty, FIRST_VALUE(SalesOrderDetailID) OVER (PARTITION BY SalesOrderID ORDER BY OrderQty ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) FstValue, LAST_VALUE(SalesOrderDetailID) OVER (PARTITION BY SalesOrderID ORDER BY OrderQty ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) LstValue FROM Sales.SalesOrderDetail s WHERE SalesOrderID IN (43670, 43669, 43667, 43663) ORDER BY s.SalesOrderID,s.SalesOrderDetailID,s.OrderQty GO Now let us see the result and ready for interesting question: Puzzle You can see that row number 2, 3, 4, and 5 has same SalesOrderID = 43667. The FIRST_VALUE is 78 and LAST_VALUE is 77. Now if these function was working on maximum and minimum value they should have given answer as 77 and 80 respectively instead of 78 and 77. Also the value of FIRST_VALUE is greater than LAST_VALUE 77. Why? Explain in detail. Hint Let me give you a simple hint. Just for simplicity I have changed the order of columns selected in the SELECT and ORDER BY (at the end). This will not change resultset but just order of the columns as well order of the rows. However, the data remains the same. USE AdventureWorks GO SELECT s.OrderQty,s.SalesOrderID,s.SalesOrderDetailID, FIRST_VALUE(SalesOrderDetailID) OVER (PARTITION BY SalesOrderID ORDER BY OrderQty ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) FstValue, LAST_VALUE(SalesOrderDetailID) OVER (PARTITION BY SalesOrderID ORDER BY OrderQty ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) LstValue FROM Sales.SalesOrderDetail s WHERE SalesOrderID IN (43670, 43669, 43667, 43663) ORDER BY s.OrderQty,s.SalesOrderID,s.SalesOrderDetailID GO Above query returns following result: Now I am very sure all of you have figured out the solution. Here is the second hint – pay attention to row 2, 3, 4, and 10. Hint2 T-SQL Enhancements: FIRST_VALUE() and LAST_VALUE() MSDN: FIRST_VALUE and LAST_VALUE Rules Leave a comment with your detailed answer by Nov 15′s blog post. Open world-wide (where Amazon ships books) If you blog about puzzle’s solution and if you win, you win additional surprise gift as well. Prizes Print copy of my new book SQL Server Interview Questions Amazon|Flipkart If you already have this book, you can opt for any of my other books SQL Wait Stats [Amazon|Flipkart|Kindle] and SQL Programming [Amazon|Flipkart|Kindle]. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Function, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology

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• Sharepoint dynamic caml query problem?

  - by AB

  Hi, I want to dynamic caml query based on query string.Let me explain it with example my query sting can be anything ?cat=ABC&cat=ABD&cat=ABE... ?Cat=ABC ?Cat=ABC&cat=ABL so no. can be anything now the problem begins I want to query my sharepoint list based on this query string if (HttpContext.Current.Request.QueryString["cat"] != null) { string _cat = HttpContext.Current.Request.QueryString["cat"].ToString(); } so this way my string contains all the query string _cat=ABC,AD,....all. I want to query my sharepoint list based on these query string and with "AND" where title=ABC and title=AD .... if there is only one query string then only where title=ABC....so I want my query string should be dynamic.... Any idea how to acheive this??

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• std::string insert method has ambiguous overloads?

  - by sdg

  Environment: VS2005 C++ using STLPort 5.1.4. Compiling the following code snippet: std::string copied = "asdf"; char ch = 's'; copied.insert(0,1,ch); I receive an error: Error 1 error C2668: 'stlpx_std::basic_string<_CharT,_Traits,_Alloc>::insert' : ambiguous call to overloaded function It appears that the problem is the insert method call on the string object. The two defined overloads are void insert ( iterator p, size_t n, char c ); string& insert ( size_t pos1, size_t n, char c ); But given that STLPort uses a simple char* as its iterator, the literal zero in the insert method in my code is ambiguous. So while I can easily overcome the problem by hinting such as copied.insert(size_t(0),1,ch); My question is: is this overloading and possible ambiguity intentional in the specification? Or more likely an unintended side-effect of the specific STLPort implementation? (Note that the Microsoft-supplied STL does not have this problem as it has a class for the iterator, instead of a naked pointer)

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• Ways to update a dependent table in the same MySQL transaction?

  - by codie

  I need to update two tables inside a single transaction. The individual queries look something like this: 1. INSERT INTO t1 (col1, col2) VALUES (val1, val2) ON DUPLICATE KEY UPDATE col2 = val2; If the above query causes an insert then I need to run the following statement on the second table: 2. INSERT INTO t2 (col1, col2) VALUES (val1, val2) ON DUPLICATE KEY UPDATE col2 = col2 + val2; otherwise, 3. UPDATE t2 SET col2 = col2 - old_val2 + val2 WHERE col1 = val1; -- old_val2 is the value of t1.col2 before it was updated Right now I run a SELECT on t1 first, to determine whether statement 1 will cause an insert or update on t1. Then I run statement 1 and either of 2 and 3 inside a transaction. What are the ways in which I can do all of these inside one transaction itself? The approach I was thinking of is the following: UPDATE t2, t1 set t2.col2 = t2.col2 - t1.col2 WHERE t1.col1 = t2.col2 and t1.col1 = val1; INSERT INTO t1 (col1, col2) VALUES (val1, val2) ON DUPLICATE KEY UPDATE col2 = val2; INSERT INTO t2, t1 (t2.col1, t2.col2) VALUES (t1.col1, t1.col2) ON DUPLICATE KEY UPDATE t2.col2 = t2.col2 + t1.col2 WHERE t1.col1 = t2.col2 and t1.col1 = val1; Unfortunately, there's no multi-table INSERT... ON DUPLICATE KEY UPDATE in MySQL 5.0. What else could I do?

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• Best way to update/insert into a table based on a remote table.

  - by martilyo

  I have two very large enterprise tables in an Oracle 10g database. One table keeps the historical information of the other table. The problem is, I'm getting to the point where the records are just too many that my insert update is taking too long and my session is getting killed by the governor. Here's a pseudocode of my update process: sqlsel := 'SELECT col1, col2, col3, sysdate FROM table2@remote_location dpi WHERE (col1, col2, col3) IN ( SELECT col1, col2, col3 FROM table2@remote_location MINUS SELECT DISTINCT col1, col2, col3 FROM table1 mpc WHERE facility = '''||load_facility||''' )'; EXECUTE IMMEDIATE sqlsel BULK COLLECT INTO table1; I've tried the MERGE statement: MERGE INTO table1 t1 USING ( SELECT col1, col2, col3 FROM table2@remote_location ) t2 ON ( t1.col1 = t2.col1 AND t1.col2 = t2.col2 AND t1.col3 = t2.col3 ) WHEN NOT MATCHED THEN INSERT (t1.col1, t1.col2, t1.col3, t1.update_dttm ) VALUES (t2.col1, t2.col2, t2.col3, sysdate ) But there seems to be a confirmed bug on versions prior to Oracle 10.2.0.4 on the merge statement when doing a merge using a remote database. The chance of getting an enterprise upgrade is slim so is there a way to further optimize my first query or write it in another way to have it run best performance wise? Thanks.

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• SQL SERVER – Update Statistics are Sampled By Default

  - by pinaldave

  After reading my earlier post SQL SERVER – Create Primary Key with Specific Name when Creating Table on Statistics, I have received another question by a blog reader. The question is as follows: Question: Are the statistics sampled by default? Answer: Yes. The sampling rate can be specified by the user and it can be anywhere between a very low value to 100%. Let us do a small experiment to verify if the auto update on statistics is left on. Also, let’s examine a very large table that is created and statistics by default- whether the statistics are sampled or not. USE [AdventureWorks] GO -- Create Table CREATE TABLE [dbo].[StatsTest]( [ID] [int] IDENTITY(1,1) NOT NULL, [FirstName] [varchar](100) NULL, [LastName] [varchar](100) NULL, [City] [varchar](100) NULL, CONSTRAINT [PK_StatsTest] PRIMARY KEY CLUSTERED ([ID] ASC) ) ON [PRIMARY] GO -- Insert 1 Million Rows INSERT INTO [dbo].[StatsTest] (FirstName,LastName,City) SELECT TOP 1000000 'Bob', CASE WHEN ROW_NUMBER() OVER (ORDER BY a.name)%2 = 1 THEN 'Smith' ELSE 'Brown' END, CASE WHEN ROW_NUMBER() OVER (ORDER BY a.name)%10 = 1 THEN 'New York' WHEN ROW_NUMBER() OVER (ORDER BY a.name)%10 = 5 THEN 'San Marino' WHEN ROW_NUMBER() OVER (ORDER BY a.name)%10 = 3 THEN 'Los Angeles' ELSE 'Houston' END FROM sys.all_objects a CROSS JOIN sys.all_objects b GO -- Update the statistics UPDATE STATISTICS [dbo].[StatsTest] GO -- Shows the statistics DBCC SHOW_STATISTICS ("StatsTest"PK_StatsTest) GO -- Clean up DROP TABLE [dbo].[StatsTest] GO Now let us observe the result of the DBCC SHOW_STATISTICS. The result shows that Resultset is for sure sampling for a large dataset. The percentage of sampling is based on data distribution as well as the kind of data in the table. Before dropping the table, let us check first the size of the table. The size of the table is 35 MB. Now, let us run the above code with lesser number of the rows. USE [AdventureWorks] GO -- Create Table CREATE TABLE [dbo].[StatsTest]( [ID] [int] IDENTITY(1,1) NOT NULL, [FirstName] [varchar](100) NULL, [LastName] [varchar](100) NULL, [City] [varchar](100) NULL, CONSTRAINT [PK_StatsTest] PRIMARY KEY CLUSTERED ([ID] ASC) ) ON [PRIMARY] GO -- Insert 1 Hundred Thousand Rows INSERT INTO [dbo].[StatsTest] (FirstName,LastName,City) SELECT TOP 100000 'Bob', CASE WHEN ROW_NUMBER() OVER (ORDER BY a.name)%2 = 1 THEN 'Smith' ELSE 'Brown' END, CASE WHEN ROW_NUMBER() OVER (ORDER BY a.name)%10 = 1 THEN 'New York' WHEN ROW_NUMBER() OVER (ORDER BY a.name)%10 = 5 THEN 'San Marino' WHEN ROW_NUMBER() OVER (ORDER BY a.name)%10 = 3 THEN 'Los Angeles' ELSE 'Houston' END FROM sys.all_objects a CROSS JOIN sys.all_objects b GO -- Update the statistics UPDATE STATISTICS [dbo].[StatsTest] GO -- Shows the statistics DBCC SHOW_STATISTICS ("StatsTest"PK_StatsTest) GO -- Clean up DROP TABLE [dbo].[StatsTest] GO You can see that Rows Sampled is just the same as Rows of the table. In this case, the sample rate is 100%. Before dropping the table, let us also check the size of the table. The size of the table is less than 4 MB. Let us compare the Result set just for a valid reference. Test 1: Total Rows: 1000000, Rows Sampled: 255420, Size of the Table: 35.516 MB Test 2: Total Rows: 100000, Rows Sampled: 100000, Size of the Table: 3.555 MB The reason behind the sample in the Test1 is that the data space is larger than 8 MB, and therefore it uses more than 1024 data pages. If the data space is smaller than 8 MB and uses less than 1024 data pages, then the sampling does not happen. Sampling aids in reducing excessive data scan; however, sometimes it reduces the accuracy of the data as well. Please note that this is just a sample test and there is no way it can be claimed as a benchmark test. The result can be dissimilar on different machines. There are lots of other information can be included when talking about this subject. I will write detail post covering all the subject very soon. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, SQL, SQL Authority, SQL Index, SQL Optimization, SQL Performance, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology Tagged: SQL Statistics

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• Mysql optimization question - How to apply AND logic in search and limit on results in one query?

  - by sandeepan-nath

  This is a little long but I have provided all the database structures and queries so that you can run it immediately and help me. Run the following queries:- CREATE TABLE IF NOT EXISTS `Tutor_Details` ( `id_tutor` int(10) NOT NULL auto_increment, `firstname` varchar(100) NOT NULL default '', `surname` varchar(155) NOT NULL default '', PRIMARY KEY (`id_tutor`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=41 ; INSERT INTO `Tutor_Details` (`id_tutor`,`firstname`, `surname`) VALUES (1, 'Sandeepan', 'Nath'), (2, 'Bob', 'Cratchit'); CREATE TABLE IF NOT EXISTS `Classes` ( `id_class` int(10) unsigned NOT NULL auto_increment, `id_tutor` int(10) unsigned NOT NULL default '0', `class_name` varchar(255) default NULL, PRIMARY KEY (`id_class`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=229 ; INSERT INTO `Classes` (`id_class`,`class_name`, `id_tutor`) VALUES (1, 'My Class', 1), (2, 'Sandeepan Class', 2); CREATE TABLE IF NOT EXISTS `Tags` ( `id_tag` int(10) unsigned NOT NULL auto_increment, `tag` varchar(255) default NULL, PRIMARY KEY (`id_tag`), UNIQUE KEY `tag` (`tag`), KEY `id_tag` (`id_tag`), KEY `tag_2` (`tag`), KEY `tag_3` (`tag`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=18 ; INSERT INTO `Tags` (`id_tag`, `tag`) VALUES (1, 'Bob'), (6, 'Class'), (2, 'Cratchit'), (4, 'Nath'), (3, 'Sandeepan'), (5, 'My'); CREATE TABLE IF NOT EXISTS `Tutors_Tag_Relations` ( `id_tag` int(10) unsigned NOT NULL default '0', `id_tutor` int(10) default NULL, KEY `Tutors_Tag_Relations` (`id_tag`), KEY `id_tutor` (`id_tutor`), KEY `id_tag` (`id_tag`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1; INSERT INTO `Tutors_Tag_Relations` (`id_tag`, `id_tutor`) VALUES (3, 1), (4, 1), (1, 2), (2, 2); CREATE TABLE IF NOT EXISTS `Class_Tag_Relations` ( `id_tag` int(10) unsigned NOT NULL default '0', `id_class` int(10) default NULL, `id_tutor` int(10) NOT NULL, KEY `Class_Tag_Relations` (`id_tag`), KEY `id_class` (`id_class`), KEY `id_tag` (`id_tag`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1; INSERT INTO `Class_Tag_Relations` (`id_tag`, `id_class`, `id_tutor`) VALUES (5, 1, 1), (6, 1, 1), (3, 2, 2), (6, 2, 2); Following is about the tables:- There are tutors who create classes. Tutor_Details - Stores tutors Classes - Stores classes created by tutors And for searching we are using a tags based approach. All the keywords are stored in tags table (while classes/tutors are created) and tag relations are entered in Tutor_Tag_Relations and Class_Tag_Relations tables (for tutors and classes respectively)like this:- Tags - id_tag tag (this is a a unique field) Tutors_Tag_Relations - Stores tag relations while the tutors are created. Class_Tag_Relations - Stores tag relations while any tutor creates a class In the present data in database, tutor "Sandeepan Nath" has has created class "My Class" and "Bob Cratchit" has created "Sandeepan Class". 3.Requirement The requirement is to return tutor records from Tutor_Details table such that all the search terms (AND logic) are present in the union of these two sets - 1. Tutor_Details table 2. classes created by a tutor in Classes table) Example search and expected results:- Search Term Result "Sandeepan Class" Tutor Sandeepan Nath's record from Tutor Details table "Class" Both the tutors from ... Most importantly, there should be only one mysql query and a LIMIT applicable on the number of results. Following is a working query which I have so far written (It just applies OR logic of search key words instead of the desired AND logic). SELECT td . * FROM Tutor_Details AS td LEFT JOIN Tutors_Tag_Relations AS ttagrels ON td.id_tutor = ttagrels.id_tutor LEFT JOIN Classes AS wc ON td.id_tutor = wc.id_tutor INNER JOIN Class_Tag_Relations AS wtagrels ON td.id_tutor = wtagrels.id_tutor LEFT JOIN Tags AS t ON t.id_tag = ttagrels.id_tag OR t.id_tag = wtagrels.id_tag WHERE t.tag LIKE '%Sandeepan%' OR t.tag LIKE '%Nath%' GROUP BY td.id_tutor LIMIT 20 Please help me with anything you can. Thanks

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• could not resolve property (complex properties)

  - by felipeoriani

  I have a asp.net mvc application with NHibernate and I do not know how to resolve a problem to query some data. I have this query: // create query var query = session.QueryOVer<Laudo>().Fetch(x => x.Equipament).Eager; // add some filters if (idEquipament.HasValue) query = query.And(x => x.Equipament.Id == idEquipament.Value); //I got the error here... if (idCompany.HasValue) query = query.And(x => x.Equipament.Company.Id == idCompany.Value); When I try to execute this query, I've got an exception with this message: "could not resolve property: Equipament.Company.Id of: DomainModel.Laudo" what can I do to fix this problem? Thanks

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• SQL SEVER – Finding Memory Pressure – External and Internal

  - by pinaldave

  Following query will provide details of external and internal memory pressure. It will return the data how much portion in the existing memory is assigned to what kind of memory type. SELECT TYPE, SUM(single_pages_kb) InternalPressure, SUM(multi_pages_kb) ExtermalPressure FROM sys.dm_os_memory_clerks GROUP BY TYPE ORDER BY SUM(single_pages_kb) DESC, SUM(multi_pages_kb) DESC GO What is your method to find memory pressure? Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Pinal Dave, SQL, SQL Authority, SQL Optimization, SQL Performance, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology

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• SQL SERVER – How to Recover SQL Database Data Deleted by Accident

  - by Pinal Dave

  In Repair a SQL Server database using a transaction log explorer, I showed how to use ApexSQL Log, a SQL Server transaction log viewer, to recover a SQL Server database after a disaster. In this blog, I’ll show you how to use another SQL Server disaster recovery tool from ApexSQL in a situation when data is accidentally deleted. You can download ApexSQL Recover here, install, and play along. With a good SQL Server disaster recovery strategy, data recovery is not a problem. You have a reliable full database backup with valid data, a full database backup and subsequent differential database backups, or a full database backup and a chain of transaction log backups. But not all situations are ideal. Here we’ll address some sub-optimal scenarios, where you can still successfully recover data. If you have only a full database backup This is the least optimal SQL Server disaster recovery strategy, as it doesn’t ensure minimal data loss. For example, data was deleted on Wednesday. Your last full database backup was created on Sunday, three days before the records were deleted. By using the full database backup created on Sunday, you will be able to recover SQL database records that existed in the table on Sunday. If there were any records inserted into the table on Monday or Tuesday, they will be lost forever. The same goes for records modified in this period. This method will not bring back modified records, only the old records that existed on Sunday. If you restore this full database backup, all your changes (intentional and accidental) will be lost and the database will be reverted to the state it had on Sunday. What you have to do is compare the records that were in the table on Sunday to the records on Wednesday, create a synchronization script, and execute it against the Wednesday database. If you have a full database backup followed by differential database backups Let’s say the situation is the same as in the example above, only you create a differential database backup every night. Use the full database backup created on Sunday, and the last differential database backup (created on Tuesday). In this scenario, you will lose only the data inserted and updated after the differential backup created on Tuesday. If you have a full database backup and a chain of transaction log backups This is the SQL Server disaster recovery strategy that provides minimal data loss. With a full chain of transaction logs, you can recover the SQL database to an exact point in time. To provide optimal results, you have to know exactly when the records were deleted, because restoring to a later point will not bring back the records. This method requires restoring the full database backup first. If you have any differential log backup created after the last full database backup, restore the most recent one. Then, restore transaction log backups, one by one, it the order they were created starting with the first created after the restored differential database backup. Now, the table will be in the state before the records were deleted. You have to identify the deleted records, script them and run the script against the original database. Although this method is reliable, it is time-consuming and requires a lot of space on disk. How to easily recover deleted records? The following solution enables you to recover SQL database records even if you have no full or differential database backups and no transaction log backups. To understand how ApexSQL Recover works, I’ll explain what happens when table data is deleted. Table data is stored in data pages. When you delete table records, they are not immediately deleted from the data pages, but marked to be overwritten by new records. Such records are not shown as existing anymore, but ApexSQL Recover can read them and create undo script for them. How long will deleted records stay in the MDF file? It depends on many factors, as time passes it’s less likely that the records will not be overwritten. The more transactions occur after the deletion, the more chances the records will be overwritten and permanently lost. Therefore, it’s recommended to create a copy of the database MDF and LDF files immediately (if you cannot take your database offline until the issue is solved) and run ApexSQL Recover on them. Note that a full database backup will not help here, as the records marked for overwriting are not included in the backup. First, I’ll delete some records from the Person.EmailAddress table in the AdventureWorks database.   I can delete these records in SQL Server Management Studio, or execute a script such as DELETE FROM Person.EmailAddress WHERE BusinessEntityID BETWEEN 70 AND 80 Then, I’ll start ApexSQL Recover and select From DELETE operation in the Recovery tab.   In the Select the database to recover step, first select the SQL Server instance. If it’s not shown in the drop-down list, click the Server icon right to the Server drop-down list and browse for the SQL Server instance, or type the instance name manually. Specify the authentication type and select the database in the Database drop-down list.   In the next step, you’re prompted to add additional data sources. As this can be a tricky step, especially for new users, ApexSQL Recover offers help via the Help me decide option.   The Help me decide option guides you through a series of questions about the database transaction log and advises what files to add. If you know that you have no transaction log backups or detached transaction logs, or the online transaction log file has been truncated after the data was deleted, select No additional transaction logs are available. If you know that you have transaction log backups that contain the delete transactions you want to recover, click Add transaction logs. The online transaction log is listed and selected automatically.   Click Add if to add transaction log backups. It would be best if you have a full transaction log chain, as explained above. The next step for this option is to specify the time range.   Selecting a small time range for the time of deletion will create the recovery script just for the accidentally deleted records. A wide time range might script the records deleted on purpose, and you don’t want that. If needed, you can check the script generated and manually remove such records. After that, for all data sources options, the next step is to select the tables. Be careful here, if you deleted some data from other tables on purpose, and don’t want to recover them, don’t select all tables, as ApexSQL Recover will create the INSERT script for them too.   The next step offers two options: to create a recovery script that will insert the deleted records back into the Person.EmailAddress table, or to create a new database, create the Person.EmailAddress table in it, and insert the deleted records. I’ll select the first one.   The recovery process is completed and 11 records are found and scripted, as expected.   To see the script, click View script. ApexSQL Recover has its own script editor, where you can review, modify, and execute the recovery script. The insert into statements look like: INSERT INTO Person.EmailAddress( BusinessEntityID, EmailAddressID, EmailAddress, rowguid, ModifiedDate) VALUES( 70, 70, N'[email protected]' COLLATE SQL_Latin1_General_CP1_CI_AS, 'd62c5b4e-c91f-403f-b630-7b7e0fda70ce', '20030109 00:00:00.000' ); To execute the script, click Execute in the menu.   If you want to check whether the records are really back, execute SELECT * FROM Person.EmailAddress WHERE BusinessEntityID BETWEEN 70 AND 80 As shown, ApexSQL Recover recovers SQL database data after accidental deletes even without the database backup that contains the deleted data and relevant transaction log backups. ApexSQL Recover reads the deleted data from the database data file, so this method can be used even for databases in the Simple recovery model. Besides recovering SQL database records from a DELETE statement, ApexSQL Recover can help when the records are lost due to a DROP TABLE, or TRUNCATE statement, as well as repair a corrupted MDF file that cannot be attached to as SQL Server instance. You can find more information about how to recover SQL database lost data and repair a SQL Server database on ApexSQL Solution center. There are solutions for various situations when data needs to be recovered. Reference: Pinal Dave (http://blog.sqlauthority.com)Filed under: PostADay, SQL, SQL Authority, SQL Backup and Restore, SQL Query, SQL Server, SQL Tips and Tricks, T SQL

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• SQL SERVER – Challenge – Puzzle – Usage of FAST Hint

  - by pinaldave

  I was recently working with various SQL Server Hints. After working for a day on various hints, I realize that for one hint, I am not able to come up with good example. The hint is FAST. Let us look at the definition of the FAST hint from the Book On-Line. FAST number_rows Specifies that the query is optimized for fast retrieval of the first number_rows. This is a nonnegative integer. After the first number_rows are returned, the query continues execution and produces its full result set. Now the question is in what condition this hint can be useful. I have tried so many different combination, I have found this hint does not make much performance difference, infect I did not notice any change in time taken to load the resultset. I noticed that this hint does not change number of the page read to return result. Now when there is difference in performance is expected because if you read the what FAST hint does is that it only returns first few results FAST – which does not mean there will be difference in performance. I also understand that this hint gives the guidance/suggestions/hint to query optimizer that there are only 100 rows are in expected resultset. This tricking the optimizer to think there are only 100 rows and which (may) lead to render different execution plan than the one which it would have taken in normal case (without hint). Again, not necessarily, this will happen always. Now if you read above discussion, you will find that basic understanding of the hint is very clear to me but I still feel that I am missing something. Here are my questions: 1) In what condition this hint can be useful? What is the case, when someone want to see first few rows early because my experience suggests that when first few rows are rendered remaining rows are rendered as well. 2) Is there any way application can retrieve the fast fetched rows from SQL Server? 3) Do you use this hint in your application? Why? When? and How? Here are few examples I have attempted during the my experiment and found there is no difference in execution plan except its estimated number of rows are different leading optimizer think that the cost is less but in reality that is not the case. USE AdventureWorks GO SET STATISTICS IO ON SET STATISTICS TIME ON GO --------------------------------------------- -- Table Scan with Fast Hint SELECT * FROM Sales.SalesOrderDetail GO SELECT * FROM Sales.SalesOrderDetail OPTION (FAST 100) GO --------------------------------------------- -- Table Scan with Where on Index Key SELECT * FROM Sales.SalesOrderDetail WHERE OrderQty = 14 GO SELECT * FROM Sales.SalesOrderDetail WHERE OrderQty = 14 OPTION (FAST 100) GO --------------------------------------------- -- Table Scan with Where on Index Key SELECT * FROM Sales.SalesOrderDetail WHERE SalesOrderDetailID < 1000 GO SELECT * FROM Sales.SalesOrderDetail WHERE SalesOrderDetailID < 1000 OPTION (FAST 100) GO Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Pinal Dave, SQL, SQL Authority, SQL Puzzle, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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• SQL SERVER – Introduction to SQL Server 2014 In-Memory OLTP

  - by Pinal Dave

  In SQL Server 2014 Microsoft has introduced a new database engine component called In-Memory OLTP aka project “Hekaton” which is fully integrated into the SQL Server Database Engine. It is optimized for OLTP workloads accessing memory resident data. In-memory OLTP helps us create memory optimized tables which in turn offer significant performance improvement for our typical OLTP workload. The main objective of memory optimized table is to ensure that highly transactional tables could live in memory and remain in memory forever without even losing out a single record. The most significant part is that it still supports majority of our Transact-SQL statement. Transact-SQL stored procedures can be compiled to machine code for further performance improvements on memory-optimized tables. This engine is designed to ensure higher concurrency and minimal blocking. In-Memory OLTP alleviates the issue of locking, using a new type of multi-version optimistic concurrency control. It also substantially reduces waiting for log writes by generating far less log data and needing fewer log writes. Points to remember Memory-optimized tables refer to tables using the new data structures and key words added as part of In-Memory OLTP. Disk-based tables refer to your normal tables which we used to create in SQL Server since its inception. These tables use a fixed size 8 KB pages that need to be read from and written to disk as a unit. Natively compiled stored procedures refer to an object Type which is new and is supported by in-memory OLTP engine which convert it into machine code, which can further improve the data access performance for memory –optimized tables. Natively compiled stored procedures can only reference memory-optimized tables, they can’t be used to reference any disk –based table. Interpreted Transact-SQL stored procedures, which is what SQL Server has always used. Cross-container transactions refer to transactions that reference both memory-optimized tables and disk-based tables. Interop refers to interpreted Transact-SQL that references memory-optimized tables. Using In-Memory OLTP In-Memory OLTP engine has been available as part of SQL Server 2014 since June 2013 CTPs. Installation of In-Memory OLTP is part of the SQL Server setup application. The In-Memory OLTP components can only be installed with a 64-bit edition of SQL Server 2014 hence they are not available with 32-bit editions. Creating Databases Any database that will store memory-optimized tables must have a MEMORY_OPTIMIZED_DATA filegroup. This filegroup is specifically designed to store the checkpoint files needed by SQL Server to recover the memory-optimized tables, and although the syntax for creating the filegroup is almost the same as for creating a regular filestream filegroup, it must also specify the option CONTAINS MEMORY_OPTIMIZED_DATA. Here is an example of a CREATE DATABASE statement for a database that can support memory-optimized tables: CREATE DATABASE InMemoryDB ON PRIMARY(NAME = [InMemoryDB_data], FILENAME = 'D:\data\InMemoryDB_data.mdf', size=500MB), FILEGROUP [SampleDB_mod_fg] CONTAINS MEMORY_OPTIMIZED_DATA (NAME = [InMemoryDB_mod_dir], FILENAME = 'S:\data\InMemoryDB_mod_dir'), (NAME = [InMemoryDB_mod_dir], FILENAME = 'R:\data\InMemoryDB_mod_dir') LOG ON (name = [SampleDB_log], Filename='L:\log\InMemoryDB_log.ldf', size=500MB) COLLATE Latin1_General_100_BIN2; Above example code creates files on three different drives (D:  S: and R:) for the data files and in memory storage so if you would like to run this code kindly change the drive and folder locations as per your convenience. Also notice that binary collation was specified as Windows (non-SQL). BIN2 collation is the only collation support at this point for any indexes on memory optimized tables. It is also possible to add a MEMORY_OPTIMIZED_DATA file group to an existing database, use the below command to achieve the same. ALTER DATABASE AdventureWorks2012 ADD FILEGROUP hekaton_mod CONTAINS MEMORY_OPTIMIZED_DATA; GO ALTER DATABASE AdventureWorks2012 ADD FILE (NAME='hekaton_mod', FILENAME='S:\data\hekaton_mod') TO FILEGROUP hekaton_mod; GO Creating Tables There is no major syntactical difference between creating a disk based table or a memory –optimized table but yes there are a few restrictions and a few new essential extensions. Essentially any memory-optimized table should use the MEMORY_OPTIMIZED = ON clause as shown in the Create Table query example. DURABILITY clause (SCHEMA_AND_DATA or SCHEMA_ONLY) Memory-optimized table should always be defined with a DURABILITY value which can be either SCHEMA_AND_DATA or  SCHEMA_ONLY the former being the default. A memory-optimized table defined with DURABILITY=SCHEMA_ONLY will not persist the data to disk which means the data durability is compromised whereas DURABILITY= SCHEMA_AND_DATA ensures that data is also persisted along with the schema. Indexing Memory Optimized Table A memory-optimized table must always have an index for all tables created with DURABILITY= SCHEMA_AND_DATA and this can be achieved by declaring a PRIMARY KEY Constraint at the time of creating a table. The following example shows a PRIMARY KEY index created as a HASH index, for which a bucket count must also be specified. CREATE TABLE Mem_Table ( [Name] VARCHAR(32) NOT NULL PRIMARY KEY NONCLUSTERED HASH WITH (BUCKET_COUNT = 100000), [City] VARCHAR(32) NULL, [State_Province] VARCHAR(32) NULL, [LastModified] DATETIME NOT NULL, ) WITH (MEMORY_OPTIMIZED = ON, DURABILITY = SCHEMA_AND_DATA); Now as you can see in the above query example we have used the clause MEMORY_OPTIMIZED = ON to make sure that it is considered as a memory optimized table and not just a normal table and also used the DURABILITY Clause= SCHEMA_AND_DATA which means it will persist data along with metadata and also you can notice this table has a PRIMARY KEY mentioned upfront which is also a mandatory clause for memory-optimized tables. We will talk more about HASH Indexes and BUCKET_COUNT in later articles on this topic which will be focusing more on Row and Index storage on Memory-Optimized tables. So stay tuned for that as well. Now as we covered the basics of Memory Optimized tables and understood the key things to remember while using memory optimized tables, let’s explore more using examples to understand the Performance gains using memory-optimized tables. I will be using the database which i created earlier in this article i.e. InMemoryDB in the below Demo Exercise. USE InMemoryDB GO -- Creating a disk based table CREATE TABLE dbo.Disktable ( Id INT IDENTITY, Name CHAR(40) ) GO CREATE NONCLUSTERED INDEX IX_ID ON dbo.Disktable (Id) GO -- Creating a memory optimized table with similar structure and DURABILITY = SCHEMA_AND_DATA CREATE TABLE dbo.Memorytable_durable ( Id INT NOT NULL PRIMARY KEY NONCLUSTERED Hash WITH (bucket_count =1000000), Name CHAR(40) ) WITH (MEMORY_OPTIMIZED = ON, DURABILITY = SCHEMA_AND_DATA) GO -- Creating an another memory optimized table with similar structure but DURABILITY = SCHEMA_Only CREATE TABLE dbo.Memorytable_nondurable ( Id INT NOT NULL PRIMARY KEY NONCLUSTERED Hash WITH (bucket_count =1000000), Name CHAR(40) ) WITH (MEMORY_OPTIMIZED = ON, DURABILITY = SCHEMA_only) GO -- Now insert 100000 records in dbo.Disktable and observe the Time Taken DECLARE @i_t bigint SET @i_t =1 WHILE @i_t<= 100000 BEGIN INSERT INTO dbo.Disktable(Name) VALUES('sachin' + CONVERT(VARCHAR,@i_t)) SET @i_t+=1 END -- Do the same inserts for Memory table dbo.Memorytable_durable and observe the Time Taken DECLARE @i_t bigint SET @i_t =1 WHILE @i_t<= 100000 BEGIN INSERT INTO dbo.Memorytable_durable VALUES(@i_t, 'sachin' + CONVERT(VARCHAR,@i_t)) SET @i_t+=1 END -- Now finally do the same inserts for Memory table dbo.Memorytable_nondurable and observe the Time Taken DECLARE @i_t bigint SET @i_t =1 WHILE @i_t<= 100000 BEGIN INSERT INTO dbo.Memorytable_nondurable VALUES(@i_t, 'sachin' + CONVERT(VARCHAR,@i_t)) SET @i_t+=1 END The above 3 Inserts took 1.20 minutes, 54 secs, and 2 secs respectively to insert 100000 records on my machine with 8 Gb RAM. This proves the point that memory-optimized tables can definitely help businesses achieve better performance for their highly transactional business table and memory- optimized tables with Durability SCHEMA_ONLY is even faster as it does not bother persisting its data to disk which makes it supremely fast. Koenig Solutions is one of the few organizations which offer IT training on SQL Server 2014 and all its updates. Now, I leave the decision on using memory_Optimized tables on you, I hope you like this article and it helped you understand  the fundamentals of IN-Memory OLTP . Reference: Pinal Dave (http://blog.sqlauthority.com)Filed under: PostADay, SQL, SQL Authority, SQL Performance, SQL Query, SQL Server, SQL Tips and Tricks, T SQL Tagged: Koenig

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• SQL SERVER – Tricks to Replace SELECT * with Column Names – SQL in Sixty Seconds #017 – Video

  - by pinaldave

  You might have heard many times that one should not use SELECT * as there are many disadvantages to the usage of the SELECT *. I also believe that there are always rare occasion when we need every single column of the query. In most of the cases, we only need a few columns of the query and we should retrieve only those columns. SELECT * has many disadvantages. Let me list a few and remaining you can add as a comment.  Retrieves unnecessary columns and increases network traffic When a new columns are added views needs to be refreshed manually Leads to usage of sub-optimal execution plan Uses clustered index in most of the cases instead of using optimal index It is difficult to debug. There are two quick tricks I have discussed in the video which explains how users can avoid using SELECT * but instead list the column names. 1) Drag the columns folder from SQL Server Management Studio to Query Editor 2) Right Click on Table Name >> Script TAble AS >> SELECT To… >> Select option It is extremely easy to list the column names in the table. In today’s sixty seconds video, you will notice that I was able to demonstrate both the methods very quickly. From now onwards there should be no excuse for not listing ColumnName. Let me ask a question back – is there ever a reason to SELECT *? If yes, would you please share that as a comment. More on SELECT *: SQL SERVER – Solution – Puzzle – SELECT * vs SELECT COUNT(*) SQL SERVER – Puzzle – SELECT * vs SELECT COUNT(*) SQL SERVER – SELECT vs. SET Performance Comparison I encourage you to submit your ideas for SQL in Sixty Seconds. We will try to accommodate as many as we can. If we like your idea we promise to share with you educational material. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Database, Pinal Dave, PostADay, SQL, SQL Authority, SQL in Sixty Seconds, SQL Query, SQL Scripts, SQL Server, SQL Server Management Studio, SQL Tips and Tricks, T SQL, Technology, Video

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• SQL SERVER – A Puzzle – Fun with NULL – Fix Error 8117

  - by pinaldave

  During my 8 years of career, I have been involved in many interviews. Quite often, I act as the  interview. If I am the interviewer, I ask many questions – from easy questions to difficult ones. When I am the interviewee, I frequently get an opportunity to ask the interviewer some questions back. Regardless of the my capacity in attending the interview, I always make it a point to ask the interviewer at least one question. What is NULL? It’s always fun to ask this question during interviews, because in every interview, I get a different answer. NULL is often confused with false, absence of value or infinite value. Honestly, NULL is a very interesting subject as it bases its behavior in server settings. There are a few properties of NULL that are universal, but the knowledge about these properties is not known in a universal sense. Let us run this simple puzzle. Run the following T-SQL script: SELECT SUM(data) FROM (SELECT NULL AS data) t It will return the following error: Msg 8117, Level 16, State 1, Line 1 Operand data type NULL is invalid for sum operator. Now the error makes it very clear that NULL is invalid for sum Operator. Frequently enough, I have showed this simple query to many folks whom I came across. I asked them if they could modify the subquery and return the result as NULL. Here is what I expected: Even though this is a very simple looking query, so far I’ve got the correct answer from only 10% of the people to whom I have asked this question. It was common for me to receive this kind of answer – convert the NULL to some data type. However, doing so usually returns the value as 0 or the integer they passed. SELECT SUM(data) FROM (SELECT ISNULL(NULL,0) AS data) t I usually see many people modifying the outer query to get desired NULL result, but that is not allowed in this simple puzzle. This small puzzle made me wonder how many people have a clear understanding about NULL. Well, here is the answer to my simple puzzle. Just CAST NULL AS INT and it will return the final result as NULL: SELECT SUM(data) FROM (SELECT CAST(NULL AS INT) AS data) t Now that you know the answer, don’t you think it was very simple indeed? This blog post is especially dedicated to my friend Madhivanan who has written an excellent blog post about NULL. I am confident that after reading the blog post from Madhivanan, you will have no confusion regarding NULL in the future. Read: NULL, NULL, NULL and nothing but NULL. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Puzzle, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology

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• SQL SERVER – Find Referenced or Referencing Object in SQL Server using sys.sql_expression_dependencies

  - by pinaldave

  A very common question which I often receive are: How do I find all the tables used in a particular stored procedure? How do I know which stored procedures are using a particular table? Both are valid question but before we see the answer of this question – let us understand two small concepts – Referenced and Referencing. Here is the sample stored procedure. CREATE PROCEDURE mySP AS SELECT * FROM Sales.Customer GO Reference: The table Sales.Customer is the reference object as it is being referenced in the stored procedure mySP. Referencing: The stored procedure mySP is the referencing object as it is referencing Sales.Customer table. Now we know what is referencing and referenced object. Let us run following queries. I am using AdventureWorks2012 as a sample database. If you do not have SQL Server 2012 here is the way to get SQL Server 2012 AdventureWorks database. Find Referecing Objects of a particular object Here we are finding all the objects which are using table Customer in their object definitions (regardless of the schema). USE AdventureWorks GO SELECT referencing_schema_name = SCHEMA_NAME(o.SCHEMA_ID), referencing_object_name = o.name, referencing_object_type_desc = o.type_desc, referenced_schema_name, referenced_object_name = referenced_entity_name, referenced_object_type_desc = o1.type_desc, referenced_server_name, referenced_database_name --,sed.* -- Uncomment for all the columns FROM sys.sql_expression_dependencies sed INNER JOIN sys.objects o ON sed.referencing_id = o.[object_id] LEFT OUTER JOIN sys.objects o1 ON sed.referenced_id = o1.[object_id] WHERE referenced_entity_name = 'Customer' The above query will return all the objects which are referencing the table Customer. Find Referenced Objects of a particular object Here we are finding all the objects which are used in the view table vIndividualCustomer. USE AdventureWorks GO SELECT referencing_schema_name = SCHEMA_NAME(o.SCHEMA_ID), referencing_object_name = o.name, referencing_object_type_desc = o.type_desc, referenced_schema_name, referenced_object_name = referenced_entity_name, referenced_object_type_desc = o1.type_desc, referenced_server_name, referenced_database_name --,sed.* -- Uncomment for all the columns FROM sys.sql_expression_dependencies sed INNER JOIN sys.objects o ON sed.referencing_id = o.[object_id] LEFT OUTER JOIN sys.objects o1 ON sed.referenced_id = o1.[object_id] WHERE o.name = 'vIndividualCustomer' The above query will return all the objects which are referencing the table Customer. I am just glad to write above query. There are more to write to this subject. In future blog post I will write more in depth about other DMV which also aids in finding referenced data. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL DMV, SQL Query, SQL Server, SQL Tips and Tricks, SQL Utility, T SQL, Technology

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• SQL SERVER – Weekly Series – Memory Lane – #048

  - 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 Order of Result Set of SELECT Statement on Clustered Indexed Table When ORDER BY is Not Used Above theory is true in most of the cases. However SQL Server does not use that logic when returning the resultset. SQL Server always returns the resultset which it can return fastest.In most of the cases the resultset which can be returned fastest is the resultset which is returned using clustered index. Effect of TRANSACTION on Local Variable – After ROLLBACK and After COMMIT One of the Jr. Developer asked me this question (What will be the Effect of TRANSACTION on Local Variable – After ROLLBACK and After COMMIT?) while I was rushing to an important meeting. I was getting late so I asked him to talk with his Application Tech Lead. When I came back from meeting both of them were looking for me. They said they are confused. I quickly wrote down following example for them. 2008 SQL SERVER – Guidelines and Coding Standards Complete List Download Coding standards and guidelines are very important for any developer on the path of a successful career. A coding standard is a set of guidelines, rules and regulations on how to write code. Coding standards should be flexible enough or should take care of the situation where they should not prevent best practices for coding. They are basically the guidelines that one should follow for better understanding. Download Guidelines and Coding Standards complete List Download Get Answer in Float When Dividing of Two Integer Many times we have requirements of some calculations amongst different fields in Tables. One of the software developers here was trying to calculate some fields having integer values and divide it which gave incorrect results in integer where accurate results including decimals was expected. Puzzle – Computed Columns Datatype Explanation SQL Server automatically does a cast to the data type having the highest precedence. So the result of INT and INT will be INT, but INT and FLOAT will be FLOAT because FLOAT has a higher precedence. If you want a different data type, you need to do an EXPLICIT cast. Renaming SP is Not Good Idea – Renaming Stored Procedure Does Not Update sys.procedures I have written many articles about renaming a tables, columns and procedures SQL SERVER – How to Rename a Column Name or Table Name, here I found something interesting about renaming the stored procedures and felt like sharing it with you all. The interesting fact is that when we rename a stored procedure using SP_Rename command, the Stored Procedure is successfully renamed. But when we try to test the procedure using sp_helptext, the procedure will be having the old name instead of new names. 2009 Insert Values of Stored Procedure in Table – Use Table Valued Function It is clear from the result set that , where I have converted stored procedure logic into the table valued function, is much better in terms of logic as it saves a large number of operations. However, this option should be used carefully. The performance of the stored procedure is “usually” better than that of functions. Interesting Observation – Index on Index View Used in Similar Query Recently, I was working on an optimization project for one of the largest organizations. While working on one of the queries, we came across a very interesting observation. We found that there was a query on the base table and when the query was run, it used the index, which did not exist in the base table. On careful examination, we found that the query was using the index that was on another view. This was very interesting as I have personally never experienced a scenario like this. In simple words, “Query on the base table can use the index created on the indexed view of the same base table.” Interesting Observation – Execution Plan and Results of Aggregate Concatenation Queries Working with SQL Server has never seemed to be monotonous – no matter how long one has worked with it. Quite often, I come across some excellent comments that I feel like acknowledging them as blog posts. Recently, I wrote an article on SQL SERVER – Execution Plan and Results of Aggregate Concatenation Queries Depend Upon Expression Location, which is well received in the community. 2010 I encourage all of you to go through complete series and write your own on the subject. If you write an article and send it to me, I will publish it on this blog with due credit to you. If you write on your own blog, I will update this blog post pointing to your blog post. SQL SERVER – ORDER BY Does Not Work – Limitation of the View 1 SQL SERVER – Adding Column is Expensive by Joining Table Outside View – Limitation of the View 2 SQL SERVER – Index Created on View not Used Often – Limitation of the View 3 SQL SERVER – SELECT * and Adding Column Issue in View – Limitation of the View 4 SQL SERVER – COUNT(*) Not Allowed but COUNT_BIG(*) Allowed – Limitation of the View 5 SQL SERVER – UNION Not Allowed but OR Allowed in Index View – Limitation of the View 6 SQL SERVER – Cross Database Queries Not Allowed in Indexed View – Limitation of the View 7 SQL SERVER – Outer Join Not Allowed in Indexed Views – Limitation of the View 8 SQL SERVER – SELF JOIN Not Allowed in Indexed View – Limitation of the View 9 SQL SERVER – Keywords View Definition Must Not Contain for Indexed View – Limitation of the View 10 SQL SERVER – View Over the View Not Possible with Index View – Limitations of the View 11 2011 Startup Parameters Easy to Configure If you are a regular reader of this blog, you must be aware that I have written about SQL Server Denali recently. Here is the quickest way to reach into the screen where we can change the startup parameters. Go to SQL Server Configuration Manager >> SQL Server Services >> Right Click on the Server >> Properties >> Startup Parameters 2012 Validating Unique Columnname Across Whole Database I sometimes come across very strange requirements and often I do not receive a proper explanation of the same. Here is the one of those examples. For example “Our business requirement is when we add new column we want it unique across current database.” Read the solution to this strange request in this blog post. Excel Losing Decimal Values When Value Pasted from SSMS ResultSet It is very common when users are coping the resultset to Excel, the floating point or decimals are missed. The solution is very much simple and it requires a small adjustment in the Excel. By default Excel is very smart and when it detects the value which is getting pasted is numeric it changes the column format to accommodate that. Basic Calculation and PEMDAS Order of Operation Read this interesting blog post for fantastic conversation about the subject. Copy Column Headers from Resultset – SQL in Sixty Seconds #027 – Video http://www.youtube.com/watch?v=x_-3tLqTRv0 Delete From Multiple Table – Update Multiple Table in Single Statement There are two questions which I get every single day multiple times. In my gmail, I have created standard canned reply for them. Let us see the questions here. I want to delete from multiple table in a single statement how will I do it? I want to update multiple table in a single statement how will I do it? Read the answer in the blog post. 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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• SQL University: Parallelism Week - Part 3, Settings and Options

  - by Adam Machanic

  Congratulations! You've made it back for the the third and final installment of Parallelism Week here at SQL University . So far we've covered the fundamentals of multitasking vs. parallel processing and delved into how parallel query plans actually work . Today we'll take a look at the settings and options that influence intra-query parallelism and discuss how best to set things up in various situations. Instance-Level Configuration Your database server probably has more than one logical processor....(read more)

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• SQL SERVER – BI Quiz Hint – Performance Tuning Cubes – Hints

  - by pinaldave

  I earlier wrote about SQL BI Quiz over here and here. The details of the quiz is here: Working with huge data is very common when it is about Data Warehousing. It is necessary to create Cubes on the data to make it meaningful and consumable. There are cases when retrieving the data from cube takes lots of the time. Let us assume that your cube is returning you data very quickly. Suddenly on one day it is returning the data very slowly. What are the three things will you to diagnose this. After diagnose what you will do to resolve performance issue. Participate in my question over here I required BI Expert Jason Thomas to help with few hints to blog readers. He is one of the leading SSAS expert and writes a complicated subject in simple words. If queries were executing properly before but now take a long time to return the data, it means that there has been a change in the environment in which it is running. Some possible changes are listed below:-  1) Data factors:- Compare the data size then and now. Increase in data can result in different execution times. Poorly written queries as well as poor design will not start showing issues till the data grows. How to find it out? (Ans : SQL Server profiler and Perfmon Counters can be used for identifying the issues and performance  tuning the MDX queries)  2) Internal Factors:- Is some slow MDX query / multiple mdx queries running at the same time, which was not running when you had tested it before? Is there any locking happening due to proactive caching or processing operations? Are the measure group caches being cleared by processing operations? (Ans : Again, profiler and perfmon counters will help in finding it out. Load testing can be done using AS Performance Workbench (http://asperfwb.codeplex.com/) by running multiple queries at once)  3) External factors:- Is some other application competing for the same resources?  HINT : Read “Identifying and Resolving MDX Query Performance Bottlenecks in SQL Server 2005 Analysis Services” (http://sqlcat.com/whitepapers/archive/2007/12/16/identifying-and-resolving-mdx-query-performance-bottlenecks-in-sql-server-2005-analysis-services.aspx) Well, these are great tips. Now win big prizes by participate in my question over here. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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• SQLbits London 2012 - Demos

  - by Adam Machanic

  Thanks to everyone who attended my sessions last Friday and Saturday at SQLbits! It was great to meet many new people, not to mention spending some time exploring one of my favorite cities, London. Attached are the demos for each of the two talks I delivered: Query Tuning Mastery: The Art of and Science of Manhandling Parallelism As a database developer, your job boils down to one word: performance. And in today's multi-core-driven world, query performance is very much determined by how well you're...(read more)

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• Is there an equivalent of jsqlparser but for SPARQL instead of SQL?

  - by Programmer

  I'm trying to use Java to construct a SPARQL query, and then send it off to a remote database. However, I'm new to both Java and SPARQL, so I was wondering if anyone could explain how to do this, rather than just posting a link. I heard there is a tool called jsqlparser for the same task, except that it's for a SQL to SPARQL conversion using Java. Conversion nor parser won't be necessary, just a method for constructing a query and querying the database provided by the user.

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