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Using sql server 2008's merge statement tech republic


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Using sql server 2008's merge statement tech republic

  1. 1. Using SQL Server 2008s MERGE statement | TechRepublic ZDNet Asia SmartPlanet TechRepublic Log In Join TechRepublic FAQ Go Pro! Blogs Downloads Newsletters Galleries Q&A Discussions News Research Library IT Management Development IT Support Data Center Networks Security Home / Blogs / The Enterprise Cloud Follow this blog: The Enterprise Cloud Using SQL Server 2008s MERGE statement By Tim Chapman September 24, 2007, 12:09 PM PDT Takeaway: SQL Server 2008’s new MERGE construct allows you to insert, update, or delete data based on certain join conditions in the same statement. Tim Chapman shows you how MERGE works with a hands-on example. SQL Server 2008’s new MERGE statement allows you to insert, update, or delete data based on certain join conditions in the same statement. In previous versions of SQL Server, you have to create separate statements if you need to insert, update, or delete data in one table based on certain conditions in another table. With MERGE, you can include the logic for these data modifications in one statement. How MERGE works The MERGE statement basically works as separate insert, update, and delete statements all within the same statement. You specify a “Source” record set and a “Target” table, and the join between the two. You then specify the type of data modification that is to occur when the records between the two data are matched or are not matched. MERGE is very useful, especially when it comes to loading data warehouse tables, which can be very large and require specific actions to be taken when rows are or are not present. MERGE example I will simulate sales feeds being received in the database and loaded to a reporting table that records daily sales statistics. In a typical scenario, the records would be loaded into a staging table (SalesFeed in this example), and then a series of transformations or DDL statements would be executed on the reporting table (SalesArchive in this example) to update the daily sales data. The MERGE statement allows you to use one statement to update the SalesArchive table rather than use several different DDL statements, which potentially could reduce the time it takes to make the updates occur, since only one lookup is done on the data rather than several. The following script creates the SalesArchive and SalesFeed tables: CREATE TABLE SalesArchive ( CustomerID INT PRIMARY KEY, SalesDate INT, TotalSalesAmount MONEY, TotalSalesCount SMALLINT, CreationDate DATETIME CONSTRAINT df_CreationDate DEFAULT(GETDATE()), UpdatedDate DATETIME CONSTRAINT df_UpdatedDate DEFAULT(GETDATE()) )[08/29/2012 3:20:12 PM]
  2. 2. Using SQL Server 2008s MERGE statement | TechRepublic CREATE TABLE SalesFeed ( CustomerID INT, Product VARCHAR(10), SaleAmount MONEY ) The script below loads some data into the SalesFeed table. The way in which I am inserting data into this table is new to SQL Server 2008; it allows you to specify many values to be inserted using the VALUES clause of the INSERT statement. INSERT INTO SalesFeed (CustomerID, Product, SaleAmount) VALUES (1,PoolTable, 1000), (2,BigScreen, 955), (3,Computer, 590), (4,BigScreen, 880), (5,Computer, 700) I have a few rows of data in my SalesFeed table and no data in my SalesArchive table. Now it is time for me to create my MERGE statement to add data to this table. Below is the MERGE script. MERGE SalesArchive AS SA USING ( SELECT CustomerID, LoadDate = MIN(CONVERT(VARCHAR(8), GETDATE(), 112)), TotalSalesAmount = SUM(SaleAmount), TotalSalesCount = COUNT(*) FROM SalesFeed GROUP BY CustomerID ) AS SalesFeedCTE (CustomerID, LoadDate, TotalSalesAmount, TotalSalesCount) ON ( SA.CustomerID = SalesFeedCTE.CustomerID AND SA.SalesDate = SalesFeedCTE.LoadDate ) WHEN NOT MATCHED THEN INSERT (CustomerID, SalesDate, TotalSalesAmount, TotalSalesCount, CreationDate, UpdatedDate) VALUES( SalesFeedCTE.CustomerID, SalesFeedCTE.LoadDate, SalesFeedCTE.TotalSalesAmount, SalesFeedCTE.TotalSalesCount, GETDATE(), GETDATE()) WHEN MATCHED THEN UPDATE SET SA.TotalSalesAmount = SA.TotalSalesAmount + SalesFeedCTE.TotalSalesAmount, SA.TotalSalesCount = SA.TotalSalesCount + SalesFeedCTE.TotalSalesCount, SA.UpdatedDate = GETDATE(); At first glance, it looks reasonably complicated, but it’s not too bad once you get used to it. The table immediately following the MERGE statement is the table that will be modified; this is known as the TARGET table. In the USING statement, data from the SalesFeed table is being aggregated inside of a subquery based on the CustomerID; this portion is known as the SOURCE. This aggregation allows me to guarantee that there will be only one record per customer to update my SalesArchive table. The ON clause of the MERGE statement is where I specify: the joining between the SOURCE, the aggregated data from the subquery, and the TARGET, the SalesArchive table. The WHEN NOT MATCHED clause is where I specify what action I want to occur when the records from the SOURCE are not found in the TARGET. In this scenario, I want to insert those records into the SalesArchive table. The WHEN MATCHED clause is where I specify what I need to occur when the records from the SalesArchive table and the subquery of the SalesFeed table are found. In this scenario, I want to update what is currently in the table for that day, such as the TotalSalesAmount, the TotalSalesCount, and the UpdatedDate. With this scenario, if another sales feed comes into the database, only one statement will need to be run for that feed. Any new customer sales will be added to the database, and any existing sales will be updated with the new sales information. Tim Chapman a SQL Server database administrator and consultant who works for a bank in Louisville, KY. Tim has more than eight years of IT experience, and he is a Microsoft certified Database Developer and Administrator. If you would like to contact Tim, please e-mail him at[08/29/2012 3:20:12 PM]
  3. 3. Using SQL Server 2008s MERGE statement | TechRepublic —————————————————————————————– Get SQL tips in your inbox TechRepublic’s free SQL Server newsletter, delivered each Tuesday, contains hands-on tips that will help you become more adept with this powerful relational database management system. Automatically subscribe today! Get IT Tips, news, and reviews delivered directly to your inbox by subscribing to TechRepublic’s free newsletters. About Tim Chapman Full Bio Contact Storage considerations for Recover lost Windows Server virtual desktops 2003 files with Volume Shadow Copy 12 Join the conversation! Add Your Opinion Comments Follow via: Staff Picks Top Rated Most Recent My Contacts See All Comments Can you merge tables across DBs same server? 0 NewToTheGame Updated - 14th Jul 2010 Votes Trying to find out if it is possible to merge table data from table on another DB on same server What syntax is required? All web examples us tables in same DB View in thread Re: Performance 0 chapman.tim@... 25th Sep 2007 Votes Youre really not going to get around the cost incurred to run the separate insert/update/delete statements. I havent ran any significant tests for this myself, but I dont think that the advantages... Read Whole Comment + View in thread Performance 0 richnorgaard@... 25th Sep 2007 Votes While I agree the table may be scanned once, the MERGE statement still invokes[08/29/2012 3:20:12 PM]
  4. 4. Using SQL Server 2008s MERGE statement | TechRepublic both an INSERT and UPDATE. The optimizer may build a special plan to leverage the lookup, but in the end the INSERT and... Read Whole Comment + View in thread See all comments Join the TechRepublic Community and join the conversation! Signing-up is free and quick, Do it now, we want to hear your opinion. Join Login[08/29/2012 3:20:12 PM]