It boils down to your understanding of the coding technique then your understanding of the problem at hand to make a decision on whether or not cursor-based processing is appropriate or not. To get started let's do the following:. The purpose for the cursor may be to update one row at a time or perform an administrative process such as SQL Server database backups in a sequential manner.
Creating a SQL Server cursor is a consistent process. Once you learn the steps you are easily able to duplicate them with various sets of logic to loop through data.
Let's walk through the steps:. From here, check out the examples below to get started on knowing when to use SQL Server cursors and how to do so. Based on the code and explanations above, let's break down the SQL Server cursor example and notate which sections would need to be updated when using this code.
The analysis below is intended to serve as insight into various scenarios where cursor-based logic may or may not be beneficial:. This tip provides sample code that can be used to expand your SQL Server cursor options beyond the syntax in this tip.
He covers the following:. The code samples in this tip are valuable to illustrate the differences between cursors in SQL Server and the While Loop. In the example above, backups are issued via a cursor. Check out these other tips that leverage cursor-based logic:. I'm still using the database backup script defined above with a few small modifications.
Always come back to read and learn additional parts to use the cursors properly. Thank you so much. One of the blessing and curses of SQL Server is that there are numerous ways to solve a problem. Knowing all of your options is important to select the best solution. There's no user input here so injection is mitigated. Microsoft did not invent cursors as you said in this article. We had them because the original relational databases were built on top of existing filesystems.
If you have ever worked with an IBM magnetic tape file system, you would immediately recognize that all of the cursor commands that we had in SQL for allocating, deallocating and using a cursor were mapped command for command from the tape files. Microsoft version of cursors was based on the UNIX version of magnetic tape drives. Later, the cursors grew to be much more complicated. I believe it was Mr. David McGovern who said, "a committee never met a feature it didn't like" and he was correct.
Jim Grey used to say in the early days of SQL, "we had no idea what the hell we were doing! Essentially, our early SQL engines were so weak the only way we could get any work done was to expose the underlying file system and give access through our language into the file system underneath it all. However, that's not the situation today. The SQL standard has been greatly expanded since the SQL — 86 standard, and includes a pretty good declarative programming language.
I hope that we will eventually deprecate everything to do with cursors in the SQL standard. This is not likely, because you need to preserve your antique features to make sure that old code will still run. Depending on the objectives of an analysis, the lead and lag functins may offer an interesting alternative to using cursors. I have not performed any testing, but my guess is that these functions may provide faster performance for analyses to which they apply.
I see it will be more easy if we used the below T-SQL it will give us all the databases not one DB with every thing we need. In table B is the new Preis for each article. Now I'd like to merge this information in one table. Thank you for the informative post. After reading through the comments, I would like to know if there is a time savings between using a cursor and using WHILE loops. I am trying to create a stored procedure in SQL Server that queries data elements from several database tables.
I need the variable definitions on both platforms. Thank you. Thank you for the feedback. Those are great points. I will try to include them in an updated version of this tip.
The first thing I would note is replacing a cursor with a while loop is a really odd thing to do as they are exactly the same thing. The second thing I would note is that Microsoft allows you to write a cursor without utilizing any of the arguments. Unfortunately most queries would execute quicker if some of the arguments were used. If would suggest using the LOCAL argument if the scope of the cursor does not extend past the current stored procedure or trigger or batch.
I need to insert column from one table to another table. I have have to add this to ssis package , so it update everyday if new column found. If I run this code, it keeps adding and duplicating same thing over and over. How do I just add once without duplicating. ON RSU. AND dmrsu. Thanks for the feedback Jeremy. I ended up rewriting the code without a cursor.
I'm sure there are many ways to do this, but I ended up creating a temp table for every month of the year. Populated each table with the data for that month from my Inventory table, then did a big join on the item numbers to get the final result set.
Below, we will show some examples where using a CURSOR creates performance issues and we will see that the same job can be done in many other ways. After a short coffee break, the query finished executing, returning rows in the time shown below.
In the cursor execution, we have two steps. Step one, the positioning, when the cursor sets its position to a row from the result set. Step two, the retrieval, when it gets the data from that specific row in an operation called the FETCH. These operations are repeated until there are no more rows to work with. Our demo tables are relative small containing roughly 1, and rows.
If we had to loop through tables with millions of rows it would last a considerable amount of time and the results would not please us. When we specify LOCAL keyword, the scope of the cursor is local to the batch in which it was created and it is valid only in this scope. After the batch finishes executing, the cursor is automatically deallocated. Also, the cursor can be referenced by a stored procedure, trigger or by a local cursor variable in a batch. View All. Vaidehi Pandere Updated date Aug 18, Opening Cursor A cursor is opened for storing data retrieved from the result set.
Fetching Cursor When a cursor is opened, rows can be fetched from the cursor one by one or in a block to do data manipulation. Closing Cursor The cursor should be closed explicitly after data manipulation. Deallocating Cursor Cursors should be deallocated to delete cursor definition and release all the system resources associated with the cursor. Why use a SQL Cursor? Cursors can be faster than a while loop but they do have more overhead.
The cursors are slower because they update tables row by row. Fetch: When the cursor is opened, rows can be fetched from the cursor one by one or in a block to perform data manipulation. Close: After data manipulation, close the cursor explicitly.
Deallocate: Finally, delete the cursor definition and release all the system resources associated with the cursor. Types of Cursors Cursors are classified depending on the circumstances in which they are opened. Skip to content. Change Language.
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