SQL Server 2008 : Viewing and Modifying Data (part 2) - Creating Stored Procedures

Stored procedures are Transact-SQL statements that perform one or more actions and are saved in the database with a name. Stored procedures, used widely to encapsulate the logic of your database system, can accept parameters and return values. Stored procedures are the only database object that can update data by executing DML statements. For example, you may write a stored procedure named AddCustomer that accepts a CustomerName, EMailAddress, and PhoneNumber parameter. The logic within this stored procedure can check that the potential customer’s details are valid, insert a new row into the Customers table using parameter values supplied, and then return the CustomerID of the newly created customer.

To create a stored procedure, use the CREATE PROCEDURE statement syntax shown in Example 3. The CREATE PROCEDURE keywords can be shortened to CREATE PROC. To change the definition or options of a stored procedure, use the ALTER PROCEDURE or ALTER PROC statement.

Example 3. CREATE PROCEDURE Statement—Syntax

CREATE PROCEDURE [schema_name].stored_procedure_name[ ; procedure_number]
[@parameter1_name parameter1_data_type [=default_parameter_value]
[ OUT | OUTPUT] [READONLY]
[@parameter2_name parameter2_data_type...]
[ WITH ENCRYPTION | RECOMPILE | EXECUTE AS]
AS [BEGIN] transact_sql_statements [END]

Stored procedures can be grouped into logical named groups. Each procedure within a group will have a unique procedure_number, while the entire group can be referred to using the procedure_name. The entire procedure group can be dropped at once using the DROP PROCEDURE statement. To use a single procedure, you can omit the procedure_number. In this case procedure_name will always be used to refer to it.

Parameters are named variables passed into the procedure. Parameter names always start with an @, and a data type must be specified for each parameter. You can also use the default_parameter_value to assign a default value to a parameter if the procedure was called without this parameter being supplied. The most common use of procedure parameters is to pass values to the stored procedure, so that it can use these values within the Transact-SQL statements that comprise it. Sometimes you must return values to the caller of your stored procedure. To do so, mark each parameter you wish to return to the caller as OUTPUT or OUT (the two are equivalent). If the parameter is not to be updated within the stored procedure, you can specify it as READONLY.

Similar to defining views, specifying the WITH ENCRYPTION option encrypts the stored procedure definition. Specify the WITH RECOMPILE option to instruct the database engine never to cache the execution plan for this stored procedure. Instead, the optimal execution plan will be calculated every time the procedure is called. The EXECUTE AS option allows you to run the procedure as an alternative set of user credentials, different from those of the caller.

Example 4 creates and executes a stored procedure to add a new row into the Stars table. The procedure accepts parameters for the star name, star type, solar mass, and description; and returns the ID of the newly created star.

Example 4. Creating and Executing a Stored Procedure

CREATE PROC AddNewStar
@ID int OUT,
@StarName varchar(50),
@SolarMass decimal(10,2),
@StarType varchar(50),
@Description ntext = 'No description provided.'
AS
BEGIN
  DECLARE @NextStarID int
  SET @NextStarID = (SELECT MAX(StarID) FROM Stars)
  SET @NextStarID = @NextStarID + 1
  INSERT dbo.Stars(StarID, StarName, SolarMass, StarType, Description)
  VALUES(@NextStarID, @StarName, @SolarMass, @StarType, @Description)
  SET @ID = @NextStarID
END;
DECLARE @NewStarID int
EXECUTE AddNewStar @NewStarID OUT, 'Sigma Octantis', 5.6, 'Giant'
SELECT @NewStarID as NewStarID
SELECT * FROM Stars
-- Results:
-- (1 row(s) affected)
-- NewStarID
-- -----------
-- 4
-- (1 row(s) affected)
-- StarID   StarName      SolarMass   StarType           Description
-- ------- -------------- ----------- --------------     ------------
-- 3       Deneb          6.00        White Supermassive Deneb is the...
                                      Giant
-- 1       Pollux         1.86        Orange Giant       Pollux,also...
-- 4       Sigma Octantis 5.60        Giant              No description...
-- 2       Sun            1.00        Yellow dwarf       No description...
--(4 row(s) affected)