sp_executesql (Transact-SQL)

Artykuł
12/03/2008

Executes a Transact-SQL statement or batch that can be reused many times, or one that has been built dynamically. The Transact-SQL statement or batch can contain embedded parameters.

Topic link icon Transact-SQL Syntax Conventions

Syntax

sp_executesql [ @stmt = ] stmt
[ 
    {, [@params=] N'@parameter_name data_type [ OUT | OUTPUT ][,...n]' } 
     {, [ @param1 = ] 'value1' [ ,...n ] }
]

Arguments

[ @stmt = ] stmt
Is a Unicode string that contains a Transact-SQL statement or batch. stmt must be either a Unicode constant or a Unicode variable. More complex Unicode expressions, such as concatenating two strings with the + operator, are not allowed. Character constants are not allowed. If a Unicode constant is specified, it must be prefixed with an N. For example, the Unicode constant N'sp_who' is valid, but the character constant 'sp_who' is not. The size of the string is limited only by available database server memory. On 64-bit servers, the size of the string is limited to 2 GB, the maximum size of nvarchar(max).

Note

stmt can contain parameters having the same form as a variable name, for example: N'SELECT * FROM HumanResources.Employee WHERE EmployeeID = @IDParameter'

Each parameter included in stmt must have a corresponding entry in both the @params parameter definition list and the parameter values list.

[ @params = ] **N'@**parameter_namedata_type[ ,... n ] '
Is one string that contains the definitions of all parameters that have been embedded in stmt. The string must be either a Unicode constant or a Unicode variable. Each parameter definition consists of a parameter name and a data type. n is a placeholder that indicates additional parameter definitions. Every parameter specified in stmt must be defined in @params. If the Transact-SQL statement or batch in stmt does not contain parameters, @params is not required. The default value for this parameter is NULL.

[ **@**param1 = ] 'value1'
Is a value for the first parameter that is defined in the parameter string. The value can be a Unicode constant or a Unicode variable. There must be a parameter value supplied for every parameter included in stmt. The values are not required when the Transact-SQL statement or batch in stmt has no parameters.

[ OUT | OUTPUT ]
Indicates that the parameter is an output parameter. text, ntext, and image parameters can be used as OUTPUT parameters, unless the procedure is a common language runtime (CLR) procedure. An output parameter that uses the OUTPUT keyword can be a cursor placeholder, unless the procedure is a CLR procedure.

n
Is a placeholder for the values of additional parameters. Values can only be constants or variables. Values cannot be more complex expressions such as functions, or expressions built by using operators.

Return Code Values

0 (success) or non-zero (failure)

Result Sets

Returns the result sets from all the SQL statements built into the SQL string.

Remarks

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.

Note

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.

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.

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:

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.
The Transact-SQL string is built only one time.
The integer parameter is specified in its native format. Casting to Unicode is not required.

Permissions

Requires membership in the public role.

Examples

A. Executing a simple SELECT statement

The following example creates and executes a simple SELECT statement that contains an embedded parameter named @level.

EXECUTE sp_executesql 
          N'SELECT * FROM AdventureWorks.HumanResources.Employee 
          WHERE ManagerID = @level',
          N'@level tinyint',
          @level = 109;

B. Executing a dynamically built string

The following example shows using sp_executesql to execute a dynamically built string. The example stored procedure is used to insert data into a set of tables that are used to partition sales data for a year. There is one table for each month of the year that has the following format:

CREATE TABLE May1998Sales
    (OrderID int PRIMARY KEY,
    CustomerID int NOT NULL,
    OrderDate  datetime NULL
        CHECK (DATEPART(yy, OrderDate) = 1998),
    OrderMonth int
        CHECK (OrderMonth = 5),
    DeliveryDate datetime  NULL,
        CHECK (DATEPART(mm, OrderDate) = OrderMonth)
    )

This sample stored procedure dynamically builds and executes an INSERT statement to insert new orders into the correct table. The example uses the order date to build the name of the table that should contain the data, and then incorporates that name into an INSERT statement.

Note

This is a simple example for sp_executesql. The example does not contain error checking and does not include checks for business rules, such as guaranteeing that order numbers are not duplicated between tables.

CREATE PROCEDURE InsertSales @PrmOrderID INT, @PrmCustomerID INT,
                 @PrmOrderDate DATETIME, @PrmDeliveryDate DATETIME
AS
DECLARE @InsertString NVARCHAR(500)
DECLARE @OrderMonth INT

-- Build the INSERT statement.
SET @InsertString = 'INSERT INTO ' +
       /* Build the name of the table. */
       SUBSTRING( DATENAME(mm, @PrmOrderDate), 1, 3) +
       CAST(DATEPART(yy, @PrmOrderDate) AS CHAR(4) ) +
       'Sales' +
       /* Build a VALUES clause. */
       ' VALUES (@InsOrderID, @InsCustID, @InsOrdDate,' +
       ' @InsOrdMonth, @InsDelDate)'

/* Set the value to use for the order month because
   functions are not allowed in the sp_executesql parameter
   list. */
SET @OrderMonth = DATEPART(mm, @PrmOrderDate)

EXEC sp_executesql @InsertString,
     N'@InsOrderID INT, @InsCustID INT, @InsOrdDate DATETIME,
       @InsOrdMonth INT, @InsDelDate DATETIME',
     @PrmOrderID, @PrmCustomerID, @PrmOrderDate,
     @OrderMonth, @PrmDeliveryDate

GO

Using sp_executesql in this procedure is more efficient than using EXECUTE to execute a string. When sp_executesql is used, there are only 12 versions of the INSERT string that are generated, one for each monthly table. With EXECUTE, each INSERT string is unique because the parameter values are different. Although both methods generate the same number of batches, the similarity of the INSERT strings generated by sp_executesql makes it more likely that the query optimizer will reuse execution plans.

C. Using the OUTPUT Parameter

The following example uses an OUTPUT parameter to store the result set generated by the SELECT statement in the @SQLString parameter. Two SELECT statements are then executed that use the value of the OUTPUT parameter.

USE AdventureWorks;
GO
DECLARE @SQLString nvarchar(500);
DECLARE @ParmDefinition nvarchar(500);
DECLARE @SalesOrderNumber nvarchar(25);
DECLARE @IntVariable int;
SET @SQLString = N'SELECT @SalesOrderOUT = MAX(SalesOrderNumber)
  FROM Sales.SalesOrderHeader
  WHERE CustomerID = @CustomerID';
SET @ParmDefinition = N'@CustomerID int,
                       @SalesOrderOUT nvarchar(25) OUTPUT';
SET @IntVariable = 22276;
EXECUTE sp_executesql
  @SQLString,
  @ParmDefinition,
  @CustomerID = @IntVariable,
  @SalesOrderOUT = @SalesOrderNumber OUTPUT;
-- This SELECT statement returns the value of the OUTPUT parameter.
SELECT @SalesOrderNumber;
-- This SELECT statement uses the value of the OUTPUT parameter in
-- the WHERE clause.
SELECT OrderDate, TotalDue
FROM Sales.SalesOrderHeader
WHERE SalesOrderNumber = @SalesOrderNumber;

Change History

Release	History
5 December 2005	New content: Added example C. Changed content: Corrected the OUTPUT parameter syntax. Changed "a variable that can be implicitly converted to ntext" in the definition of stmt and parameter_name to "a Unicode variable."

5 December 2005

New content:

Added example C.

Changed content:

Corrected the OUTPUT parameter syntax.
Changed "a variable that can be implicitly converted to ntext" in the definition of stmt and parameter_name to "a Unicode variable."

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