sp_executesql has the same behavior as EXECUTE with regard to batches, the scope of names, and database context. The Transact-SQL statement or batch in the sp_executesql stmt parameter is not compiled until the sp_executesql statement is executed. The contents of stmt are then compiled and executed as an execution plan separate from the execution plan of the batch that called sp_executesql. The sp_executesql batch cannot reference variables declared in the batch that calls sp_executesql. Local cursors or variables in the sp_executesql batch are not visible to the batch that calls sp_executesql. Changes in database context last only to the end of the sp_executesql statement.
sp_executesql can be used instead of stored procedures to execute a Transact-SQL statement many times when the change in parameter values to the statement is the only variation. Because the Transact-SQL statement itself remains constant and only the parameter values change, the SQL Server query optimizer is likely to reuse the execution plan it generates for the first execution.
.gif) Note: |
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To improve performance use fully qualified object names in the statement string. |
sp_executesql supports the setting of parameter values separately from the Transact-SQL string as shown in the following example.
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DECLARE @IntVariable int;
DECLARE @SQLString nvarchar(500);
DECLARE @ParmDefinition nvarchar(500);
/* Build the SQL string one time.*/
SET @SQLString =
N'SELECT EmployeeID, NationalIDNumber, Title, ManagerID
FROM AdventureWorks.HumanResources.Employee
WHERE ManagerID = @ManagerID';
SET @ParmDefinition = N'@ManagerID tinyint';
/* Execute the string with the first parameter value. */
SET @IntVariable = 197;
EXECUTE sp_executesql @SQLString, @ParmDefinition,
@ManagerID = @IntVariable;
/* Execute the same string with the second parameter value. */
SET @IntVariable = 109;
EXECUTE sp_executesql @SQLString, @ParmDefinition,
@ManagerID = @IntVariable; |
Output parameters can also be used with sp_executesql. The following example retrieves a job title from the AdventureWorks.HumanResources.Employee table and returns it in the output parameter @max_title.
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DECLARE @IntVariable int;
DECLARE @SQLString nvarchar(500);
DECLARE @ParmDefinition nvarchar(500);
DECLARE @max_title varchar(30);
SET @IntVariable = 197;
SET @SQLString = N'SELECT @max_titleOUT = max(Title)
FROM AdventureWorks.HumanResources.Employee
WHERE ManagerID = @level';
SET @ParmDefinition = N'@level tinyint, @max_titleOUT varchar(30) OUTPUT';
EXECUTE sp_executesql @SQLString, @ParmDefinition, @level = @IntVariable, @max_titleOUT=@max_title OUTPUT;
SELECT @max_title; |
Being able to substitute parameters in sp_executesql offers the following advantages to using the EXECUTE statement to execute a string:
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Because the actual text of the Transact-SQL statement in the sp_executesql string does not change between executions, the query optimizer will probably match the Transact-SQL statement in the second execution with the execution plan generated for the first execution. Therefore, SQL Server does not have to compile the second statement.
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The Transact-SQL string is built only one time.
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The integer parameter is specified in its native format. Casting to Unicode is not required.