Return Data from a Stored Procedure
There are three ways of returning data from a procedure to a calling program: result sets, output parameters, and return codes. This topic provides information on the three approaches.
Returning Data Using Result Sets
If you include a SELECT statement in the body of a stored procedure (but not a SELECT ... INTO or INSERT ... SELECT), the rows specified by the SELECT statement will be sent directly to the client. For large result sets the stored procedure execution will not continue to the next statement until the result set has been completely sent to the client. For small result sets the results will be spooled for return to the client and execution will continue. If multiple such SELECT statements are run during the exeuction of the stored proceudre, multiple result sets will be sent to the client. This behavior also applies to nested TSQL batches, nested stored procedures and top-level TSQL batches.
Examples of Returning Data Using a Result Set
The following example shows a stored procedure that returns the LastName and SalesYTD values for all SalesPerson rows that also appear in the vEmployee view.
USE AdventureWorks2012; GO IF OBJECT_ID('Sales.uspGetEmployeeSalesYTD', 'P') IS NOT NULL DROP PROCEDURE Sales.uspGetEmployeeSalesYTD; GO CREATE PROCEDURE Sales.uspGetEmployeeSalesYTD AS SET NOCOUNT ON; SELECT LastName, SalesYTD FROM Sales.SalesPerson AS sp JOIN HumanResources.vEmployee AS e ON e.BusinessEntityID = sp.BusinessEntityID RETURN GO
Returning Data Using an Output Parameter
If you specify the OUTPUT keyword for a parameter in the procedure definition, the procedure can return the current value of the parameter to the calling program when the procedure exits. To save the value of the parameter in a variable that can be used in the calling program, the calling program must use the OUTPUT keyword when executing the procedure. For more information about what data types can be used as output parameters, see CREATE PROCEDURE (Transact-SQL).
Examples of Output Parameter
The following example shows a procedure with an input and an output parameter. The
@SalesPerson parameter would receive an input value specified by the calling program. The SELECT statement uses the value passed into the input parameter to obtain the correct
SalesYTD value. The SELECT statement also assigns the value to the
@SalesYTD output parameter, which returns the value to the calling program when the procedure exits.
USE AdventureWorks2012; GO IF OBJECT_ID('Sales.uspGetEmployeeSalesYTD', 'P') IS NOT NULL DROP PROCEDURE Sales.uspGetEmployeeSalesYTD; GO CREATE PROCEDURE Sales.uspGetEmployeeSalesYTD @SalesPerson nvarchar(50), @SalesYTD money OUTPUT AS SET NOCOUNT ON; SELECT @SalesYTD = SalesYTD FROM Sales.SalesPerson AS sp JOIN HumanResources.vEmployee AS e ON e.BusinessEntityID = sp.BusinessEntityID WHERE LastName = @SalesPerson; RETURN GO
The following example calls the procedure created in the first example and saves the output value returned from the called procedure in the
@SalesYTD variable, which is local to the calling program.
-- Declare the variable to receive the output value of the procedure. DECLARE @SalesYTDBySalesPerson money; -- Execute the procedure specifying a last name for the input parameter -- and saving the output value in the variable @SalesYTDBySalesPerson EXECUTE Sales.uspGetEmployeeSalesYTD N'Blythe', @SalesYTD = @SalesYTDBySalesPerson OUTPUT; -- Display the value returned by the procedure. PRINT 'Year-to-date sales for this employee is ' + convert(varchar(10),@SalesYTDBySalesPerson); GO
Input values can also be specified for OUTPUT parameters when the procedure is executed. This allows the procedure to receive a value from the calling program, change or perform operations with the value, and then return the new value to the calling program. In the previous example, the
@SalesYTDBySalesPerson variable can be assigned a value before the program calls the
Sales.uspGetEmployeeSalesYTD procedure. The execute statement would pass the
@SalesYTDBySalesPerson variable value into the
@SalesYTD OUTPUT parameter. Then in the procedure body, the value could be used for calculations that generate a new value. The new value would be passed back out of the procedure through the OUTPUT parameter, updating the value in the
@SalesYTDBySalesPerson variable when the procedure exits. This is often referred to as "pass-by-reference capability."
If you specify OUTPUT for a parameter when you call a procedure and that parameter is not defined by using OUTPUT in the procedure definition, you get an error message. However, you can execute a procedure with output parameters and not specify OUTPUT when executing the procedure. No error is returned, but you cannot use the output value in the calling program.
Using the Cursor Data Type in OUTPUT Parameters
Transact-SQL procedures can use the cursor data type only for OUTPUT parameters. If the cursor data type is specified for a parameter, both the VARYING and OUTPUT keywords must be specified for that parameter in the procedure definition. A parameter can be specified as only OUTPUT but if the VARYING keyword is specified in the parameter declaration, the data type must be cursor and the OUTPUT keyword must also be specified.
The cursor data type cannot be bound to application variables through the database APIs such as OLE DB, ODBC, ADO, and DB-Library. Because OUTPUT parameters must be bound before an application can execute a procedure, procedures with cursor OUTPUT parameters cannot be called from the database APIs. These procedures can be called from Transact-SQL batches, procedures, or triggers only when the cursor OUTPUT variable is assigned to a Transact-SQL local cursor variable.
Rules for Cursor Output Parameters
The following rules pertain to cursor output parameters when the procedure is executed:
For a forward-only cursor, the rows returned in the cursor's result set are only those rows at and beyond the position of the cursor at the conclusion of the procedure execution, for example:
A nonscrollable cursor is opened in a procedure on a result set named RS of 100 rows.
The procedure fetches the first 5 rows of result set RS.
The procedure returns to its caller.
The result set RS returned to the caller consists of rows from 6 through 100 of RS, and the cursor in the caller is positioned before the first row of RS.
For a forward-only cursor, if the cursor is positioned before the first row when the procedure exits, the entire result set is returned to the calling batch, procedure, or trigger. When returned, the cursor position is set before the first row.
For a forward-only cursor, if the cursor is positioned beyond the end of the last row when the procedure exits, an empty result set is returned to the calling batch, procedure, or trigger.
An empty result set is not the same as a null value.
For a scrollable cursor, all the rows in the result set are returned to the calling batch, procedure, or trigger when the procedure exits. When returned, the cursor position is left at the position of the last fetch executed in the procedure.
For any type of cursor, if the cursor is closed, then a null value is passed back to the calling batch, procedure, or trigger. This will also be the case if a cursor is assigned to a parameter, but that cursor is never opened.
The closed state matters only at return time. For example, it is valid to close a cursor part of the way through the procedure, to open it again later in the procedure, and return that cursor's result set to the calling batch, procedure, or trigger.
Examples of Cursor Output Parameters
In the following example, a procedure is created that specified an output parameter,
@currency_cursor using the cursor data type. The procedure is then called in a batch.
First, create the procedure that declares and then opens a cursor on the Currency table.
USE AdventureWorks2012; GO IF OBJECT_ID ( 'dbo.uspCurrencyCursor', 'P' ) IS NOT NULL DROP PROCEDURE dbo.uspCurrencyCursor; GO CREATE PROCEDURE dbo.uspCurrencyCursor @CurrencyCursor CURSOR VARYING OUTPUT AS SET NOCOUNT ON; SET @CurrencyCursor = CURSOR FORWARD_ONLY STATIC FOR SELECT CurrencyCode, Name FROM Sales.Currency; OPEN @CurrencyCursor; GO
Next, execute a batch that declares a local cursor variable, executes the procedure to assign the cursor to the local variable, and then fetches the rows from the cursor.
USE AdventureWorks2012; GO DECLARE @MyCursor CURSOR; EXEC dbo.uspCurrencyCursor @CurrencyCursor = @MyCursor OUTPUT; WHILE (@@FETCH_STATUS = 0) BEGIN; FETCH NEXT FROM @MyCursor; END; CLOSE @MyCursor; DEALLOCATE @MyCursor; GO
Returning Data Using a Return Code
A procedure can return an integer value called a return code to indicate the execution status of a procedure. You specify the return code for a procedure using the RETURN statement. As with OUTPUT parameters, you must save the return code in a variable when the procedure is executed in order to use the return code value in the calling program. For example, the assignment variable
@result of data type int is used to store the return code from the procedure
my_proc, such as:
DECLARE @result int; EXECUTE @result = my_proc;
Return codes are commonly used in control-of-flow blocks within procedures to set the return code value for each possible error situation. You can use the @@ERROR function after a Transact-SQL statement to detect whether an error occurred during the execution of the statement. Before the introduction of TRY/CATCH/THROW error handling in TSQL return codes were sometimes required to determine the success or failure of stored procedures. Stored Procedures should always indicate failure with an error (generated with THROW/RAISERROR if necessary), and not rely on a return code to indicate the failure. Also you should avoid using the return code to return application data.
Examples of Return Codes
The following example shows the
usp_GetSalesYTD procedure with error handling that sets special return code values for various errors. The following table shows the integer value that is assigned by the procedure to each possible error, and the corresponding meaning for each value.
|Return code value||Meaning|
|1||Required parameter value is not specified.|
|2||Specified parameter value is not valid.|
|3||Error has occurred getting sales value.|
|4||NULL sales value found for the salesperson.|
USE AdventureWorks2012; GO IF OBJECT_ID('Sales.usp_GetSalesYTD', 'P') IS NOT NULL DROP PROCEDURE Sales.usp_GetSalesYTD; GO CREATE PROCEDURE Sales.usp_GetSalesYTD @SalesPerson nvarchar(50) = NULL, -- NULL default value @SalesYTD money = NULL OUTPUT AS -- Validate the @SalesPerson parameter. IF @SalesPerson IS NULL BEGIN PRINT 'ERROR: You must specify a last name for the sales person.' RETURN(1) END ELSE BEGIN -- Make sure the value is valid. IF (SELECT COUNT(*) FROM HumanResources.vEmployee WHERE LastName = @SalesPerson) = 0 RETURN(2) END -- Get the sales for the specified name and -- assign it to the output parameter. SELECT @SalesYTD = SalesYTD FROM Sales.SalesPerson AS sp JOIN HumanResources.vEmployee AS e ON e.BusinessEntityID = sp.BusinessEntityID WHERE LastName = @SalesPerson; -- Check for SQL Server errors. IF @@ERROR <> 0 BEGIN RETURN(3) END ELSE BEGIN -- Check to see if the ytd_sales value is NULL. IF @SalesYTD IS NULL RETURN(4) ELSE -- SUCCESS!! RETURN(0) END -- Run the stored procedure without specifying an input value. EXEC Sales.usp_GetSalesYTD; GO -- Run the stored procedure with an input value. DECLARE @SalesYTDForSalesPerson money, @ret_code int; -- Execute the procedure specifying a last name for the input parameter -- and saving the output value in the variable @SalesYTD EXECUTE Sales.usp_GetSalesYTD N'Blythe', @SalesYTD = @SalesYTDForSalesPerson OUTPUT; PRINT N'Year-to-date sales for this employee is ' + CONVERT(varchar(10), @SalesYTDForSalesPerson);
The following example creates a program to handle the return codes that are returned from the
-- Declare the variables to receive the output value and return code -- of the procedure. DECLARE @SalesYTDForSalesPerson money, @ret_code int; -- Execute the procedure with a title_id value -- and save the output value and return code in variables. EXECUTE @ret_code = Sales.usp_GetSalesYTD N'Blythe', @SalesYTD = @SalesYTDForSalesPerson OUTPUT; -- Check the return codes. IF @ret_code = 0 BEGIN PRINT 'Procedure executed successfully' -- Display the value returned by the procedure. PRINT 'Year-to-date sales for this employee is ' + CONVERT(varchar(10),@SalesYTDForSalesPerson) END ELSE IF @ret_code = 1 PRINT 'ERROR: You must specify a last name for the sales person.' ELSE IF @ret_code = 2 PRINT 'ERROR: You must enter a valid last name for the sales person.' ELSE IF @ret_code = 3 PRINT 'ERROR: An error occurred getting sales value.' ELSE IF @ret_code = 4 PRINT 'ERROR: No sales recorded for this employee.' GO