SQL Server 2008 R2 : Advantages of Stored Procedures, Creating Stored Procedures

Note

You can use stored procedures to make a database sort of a “black box” as far as the developers and the application code are concerned. If all database access is managed through stored procedures, the applications are shielded from possible changes to the underlying database structures.

For example, one organization found the need to split one table across multiple databases. By simply modifying the existing stored procedures to handle the multiple tables and by using distributed partitioned views, the company was able to make this change without requiring any changes to the front-end application code.

2. Creating Stored Procedures

To create a stored procedure, you need to give the procedure a unique name within the schema and then write the sequence of SQL statements to be executed within the procedure. Following is the basic syntax for creating stored procedures:

CREATE { PROC | PROCEDURE } [schema_name.]procedure_name [ ; number ]
    [ { @parameter [ schema_name.]data_type }
        [ VARYING ] [ = default ] [ OUT | OUTPUT ] [READONLY]
    ] [ ,...n ]
[ WITH  {  [ ENCRYPTION ]
         , [ RECOMPILE ]
         , [ EXECUTE_AS_Clause ]
         [ ,...n] ]
[ FOR REPLICATION ]
AS
[BEGIN]
    SQL_Statements
[   RETURN scalar_expression ]
[END]

It is good programming practice to always end a procedure with the RETURN statement and to specify a return status other than 0 when an error condition occurs. Listing 1 shows a simple stored procedure that returns book titles and the names of the authors who wrote them.

Listing 1. A Sample Stored Procedure

use bigpubs2008
go
IF EXISTS ( SELECT * FROM sys.procedures
               WHERE schema_id = schema_id('dbo')
                 AND name = N'title_authors')
   DROP PROCEDURE dbo.title_authors
GO
CREATE PROCEDURE title_authors
AS
BEGIN
   SELECT a.au_lname, a.au_fname, t.title
      FROM titles t INNER JOIN
           titleauthor ta ON t.title_id = ta.title_id RIGHT OUTER JOIN
           authors a ON ta.au_id = a.au_id
   RETURN 0
END

Creating Procedures in SSMS

To create a stored procedure in SSMS, open the object tree for the database in which you want to create the procedure, open the Programmability folder, right-click the Stored Procedures folder, and from the context menu, choose New Stored Procedure. SSMS opens a new query window, populated with code that is based on a default template for stored procedures. Listing 2 shows an example of the default template code for a stored procedure that would be opened into a new query window.

Listing 2. An Example of a New Stored Procedure Creation Script Generated by SSMS

-- ================================================
-- Template generated from Template Explorer using:
-- Create Procedure (New Menu).SQL
--
-- Use the Specify Values for Template Parameters
-- command (Ctrl-Shift-M) to fill in the parameter
-- values below.
--
-- This block of comments will not be included in
-- the definition of the procedure.
-- ================================================
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
-- =============================================
-- Author:          <Author,,Name>
-- Create date: <Create Date,,>
-- Description:     <Description,,>
-- =============================================
CREATE PROCEDURE <Procedure_Name, sysname, ProcedureName>
     - Add the parameters for the stored procedure here
     <@Param1, sysname, @p1> <Datatype_For_Param1, , int> =
 <Default_Value_For_Param1, , 0>,
     <@Param2, sysname, @p2> <Datatype_For_Param2, , int> =
 <Default_Value_For_Param2, , 0>
AS
BEGIN
     - SET NOCOUNT ON added to prevent extra result sets from
     - interfering with SELECT statements.
     SET NOCOUNT ON;

     -- Insert statements for procedure here
     SELECT <@Param1, sysname, @p1>, <@Param2, sysname, @p2>
END
GO


					  

You can modify the template code as necessary to set the procedure name and to specify the parameters, return value, and procedure body. When you are finished, you can execute the contents of the query window to create the procedure. After you have created the procedure successfully, it is recommended that you save the source code to a file by choosing the Save or Save As option from the File menu. This way, you can re-create the stored procedure from the file if it is accidentally dropped from the database.

One thing you might notice about the stored procedure template is that it contains template parameters for parameter names, procedure name, author name, create date, and so on. These template parameters are in the format <parameter, type, value>:

• parameter_name is the name of the template parameter in the script.

• data_type is the optional data type of the template parameter.

• value is the default value to be used to replace every occurrence of the template parameter in the script

You can auto substitute values for template parameters by selecting Query, Specify Values for Template Parameters or by pressing Ctrl+Shift+M. This brings up the dialog shown in Figure 1.

You enter the values for the template parameters in the Value column and then click OK. SSMS then substitutes any values you specified wherever the template parameter is used within the template.

An alternative way to create a stored procedure from a template is to use the Template Explorer in SSMS. You can open the Template Explorer by selecting View, Template Explorer in SSMS or by pressing Ctrl+Alt+T. The Template Explorer window appears in SSMS, as shown in Figure 2.

Figure 2. Using the Template Explorer for creating stored procedures in SSMS.

You can double-click the name of the stored procedure template you want to use or right-click the desired template and then select Open. SSMS opens a new query window, populated with the template code.

Creating Custom Stored Procedure Templates

To create a custom stored procedure template, right-click the Stored Procedure folder in the Template Explorer and select New. SSMS then creates an entry in the Template Explorer, and you can specify the name for the template.

To begin adding code to the template, right-click the template and select Edit. This opens a query window in which you can start entering the new template code. Probably the best way to get started is to copy the template code from one of the templates provided with SQL Server 2008 and then modify it as you desire. You then select File, Save to save the template code to the file.

Listing 3 shows an example of a new stored procedure template.

Listing 3. An Example of Custom Stored Procedure Template

-- =============================================
-- Create basic stored procedure template
-- =============================================

-- Drop stored procedure if it already exists
IF EXISTS (
  SELECT *
    FROM sys.procedures
   WHERE schema_id = schema_id('dbo')
     AND name = N'<Proc_Name, sysname, myproc>'
)
   DROP PROCEDURE <Schema_Name, sysname, dbo>.<Proc_Name, sysname, myproc>
GO
-- =============================================
-- Author:         <Author,,Name>
-- Create date: <Create Date,,>
-- Description:    <Description,,>
-- =============================================
CREATE PROCEDURE <Schema_Name, sysname, dbo>.<Proc_Name, sysname, myproc>
    — Add the parameters for the stored procedure here
    <@param1, sysname, @p1> <param1_type, , int> = <param1_default, , 0>,
    <@param2, sysname, @p2> <param2_type, , int> = <param2_default, , 0>,
    <@param3, sysname, @p3> <param3_type, , int>  OUTPUT
AS
BEGIN
    -- SET NOCOUNT ON added to prevent extra result sets from
    -- interfering with SELECT statements.
    SET NOCOUNT ON;

    DECLARE @trancnt int
    SELECT @trancnt = @@TRANCOUNT

    if @trancnt = 0
        BEGIN TRAN <Proc_Name, sysname, myproc>
    else
        SAVE TRAN <Proc_Name, sysname, myproc>

    /* Insert processing code here */

    if (@@error != 0) -- check for error condition
    begin
        -- rollback to savepoint, or begin tran
        rollback tran <Proc_Name, sysname, myproc>
        -- return error code indicating rollback
        return -101
    end

    /* Insert more processing here if required */


    -- set value of output parameter
    set <@param3,sysname, @p3> = <@param1,sysname, @p1> + <@param2,sysname, @p2>

    if @trancnt = 0     -- this proc issued begin tran
      -- commit tran, decrement @@trancount to 0
      commit tran <Proc_Name, sysname, myproc>
    -- commit not required with save tran

    return 0 /* successful return */

END
GO


— =============================================
— Example to execute the stored procedure
— =============================================
DECLARE <@output_variable, sysname, @p3_output> <output_datatype, , int>

EXECUTE <Schema_name, sysname, dbo>.<Proc_name, sysname, myproc>
        <@param1, sysname, @p1> = <param1_value, , 1>,
        <@param2, sysname, @p2> = <param2_value, , 1>,
        <@param3, sysname, @p3> = <@output_variable, sysname, @p3_output> OUTPUT

SELECT <@output_variable, sysname, @p3_output>
GO


					  

After you define a custom stored procedure template, you can use it as you would use the built-in templates. You can double-click it or right-click and select Open, and SSMS opens a new query window with a new stored procedure creation script based on the custom template. If you use the default values for the template parameters, after the parameter substitution, the CREATE PROCEDURE script looks like the one in Listing 4.

Listing 4. An Example of a CREATE PROCEDURE Script Generated from the Custom Stored Procedure Template

-- =============================================
-- Create basic stored procedure template
-- =============================================

-- Drop stored procedure if it already exists
IF EXISTS (
  SELECT *
    FROM sys.procedures
   WHERE schema_id = schema_id('dbo')
     AND name = N'myproc'
)
   DROP PROCEDURE dbo.myproc
GO

-- =============================================
-- Author:         Name
-- Create date:
-- Description:
-- =============================================
CREATE PROCEDURE dbo.myproc
    — Add the parameters for the stored procedure here
    @p1 int = 0,
    @p2 int = 0,
    @p3 int  OUTPUT
AS
BEGIN
    -- SET NOCOUNT ON added to prevent extra result sets from
    -- interfering with SELECT statements.
    SET NOCOUNT ON;

    DECLARE @trancnt int
    SELECT @trancnt = @@TRANCOUNT

    if @trancnt = 0
        BEGIN TRAN myproc
    else
        SAVE TRAN myproc

    /* Insert processing code here */

    if (@@error != 0) -- check for error condition
    begin
        -- rollback to savepoint, or begin tran
        rollback tran myproc
        -- return error code indicating rollback
        return -101
    end

    /* Insert more processing here if required */
    -- set value of output parameter
    set @p3 = @p1 + @p2

    if @trancnt = 0     -- this proc issued begin tran
      -- commit tran, decrement @@trancount to 0
      commit tran myproc
    -- commit not required with save tran

    return 0 /* successful return */

END
GO


-- =============================================
-- Example to execute the stored procedure
-- =============================================
DECLARE @p3_output int

EXECUTE dbo.myproc
        @p1 = 1,
        @p2 = 1,
        @p3 = @p3_output OUTPUT

SELECT @p3_output
GO


					  

Temporary Stored Procedures

SQL Server enables you to create private and global temporary stored procedures. Temporary stored procedures are analogous to temporary tables in that they can be created with the # and ## prefixes added to the procedure name. The # prefix denotes a local temporary stored procedure; ## denotes a global temporary stored procedure. A local temporary stored procedure can be executed only by the connection that created it, and the procedure is automatically deleted when the connection is closed. A global temporary stored procedure can be accessed by multiple connections and exists until the connection used by the user who created the procedure is closed and any currently executing versions of the procedure by any other connections are completed.

If a stored procedure not prefixed with # or ## is created directly in the tempdb database, the stored procedure exists until SQL Server is shut down. Procedures created directly in tempdb continue to exist even after the creating connection is terminated.

Temporary stored procedures are provided for backward compatibility with earlier versions of SQL Server that did not support the reuse of execution plans for T-SQL statements or batches. Applications connecting to SQL Server 2000 and higher should use the sp_executesql system stored procedure to execute dynamic SQL statements instead of creating temporary stored procedures.