The SET ROWCOUNT statement in SQL Server is a useful tool that allows you to limit the number of records returned to the client during a single connection. By specifying a row count, SQL Server will stop processing the query as soon as the specified number of rows is found. This can be particularly helpful when dealing with large datasets or when you only need a subset of the results.
The syntax for the SET ROWCOUNT statement is as follows:
SET ROWCOUNT 10
SELECT *
FROM dbo.Orders
WHERE EmployeeID = 5
ORDER BY OrderDate
SET ROWCOUNT 0To turn off the row count limit and return all rows, you can specify SET ROWCOUNT 0.
It’s important to note that the ROWCOUNT option is ignored for INSERT, UPDATE, and DELETE statements against remote tables and local, remote partitioned views. It is also ignored when an explicit TOP expression is used in the same statement. This includes statements in which INSERT is followed by a SELECT clause. Additionally, the SET ROWCOUNT statement overrides the SELECT statement’s TOP keyword if the row count is the smaller value.
When you set the ROWCOUNT option, it causes most Transact-SQL statements to stop processing once they have been affected by the specified number of rows. This includes triggers and data modification statements such as INSERT, UPDATE, and DELETE. However, it does not affect dynamic cursors, but it does limit the rowset of keyset and insensitive cursors.
It’s important to use the SET ROWCOUNT option with caution and primarily with the SELECT statement. The setting of SET ROWCOUNT is determined at execute or run time, not at parse time.
Here are some interesting facts about the SET ROWCOUNT statement:
- It cannot be used in a User-Defined Function (UDF), but the current ROWCOUNT limit setting of its caller will be applied to the SELECT statements in the UDF.
- When SET ROWCOUNT n applies to a SELECT statement with sub-queries, the results and ordering are always guaranteed.
- To avoid confusion and unexpected logical errors, it’s recommended to turn SET ROWCOUNT n on just before the final SELECT statement that returns the records.
In SQL Server 2005, the SET ROWCOUNT statement has the same behavior as in SQL Server 2000. However, it is generally recommended to use the TOP (n) clause instead of the SET ROWCOUNT statement in newer versions of SQL Server.
Overall, the SET ROWCOUNT statement is a powerful tool in SQL Server that allows you to control the number of records returned in a query. By understanding its syntax and limitations, you can effectively manage large datasets and improve query performance.