Tài liệu Introducing Stored Procedures doc

You'll typically create a stored procedure when you need to perform a task that intensively uses the database, or you want to centralize code in the database that any user can call rathe

Introducing Stored Procedures

SQL Server allows you to store procedures in a database Stored procedures differ from user-defined functions in that procedures can return a much wider array of data types

You'll typically create a stored procedure when you need to perform a task that

intensively uses the database, or you want to centralize code in the database that any user can call rather than have each user write their own program to perform the same task One example of intensive database use is a banking application by which you need to update accounts at the end of each day One example of when you'd use centralized code

is when you want to restrict user access to database tables: you might want users to be able to add a row to a table only through a procedure so that no mistakes are made

In this section, you'll learn how to create a stored procedure in the Northwind database and run it using the Query Analyzer tool

Creating a Stored Procedure

The procedure you'll see in this section is named AddProduct() This procedure adds a row to the Products table, setting the column values for the new row to those passed as parameters to the procedure

The ProductID column for the new row is assigned a value automatically by the database through the use of an identity that was set up when the table was originally created This identity value may be read using the @@IDENTITY function after the new row is added

to the table The AddProduct() procedure you'll see here returns that identity value to the calling statement

You create a procedure using the CREATE PROCEDURE statement, and Listing 4.5

shows the AddProduct.sql script that creates the AddProduct() procedure

Listing 4.5: ADDPRODUCT.SQL

/*

AddProduct.sql creates a procedure that adds a row to the

Products table using values passed as parameters to the

procedure The procedure returns the ProductID of the new row

*/

CREATE PROCEDURE AddProduct

@MyProductName nvarchar(40),

@MySupplierID int,

@MyCategoryID int,

@MyQuantityPerUnit nvarchar(20),

@MyUnitPrice money,

@MyUnitsInStock smallint,

@MyUnitsOnOrder smallint,

@MyReorderLevel smallint,

@MyDiscontinued bit

AS

DECLARE @ProductID int

insert a row into the Products table

INSERT INTO Products (

ProductName, SupplierID, CategoryID, QuantityPerUnit,

UnitPrice, UnitsInStock, UnitsOnOrder, ReorderLevel,

Discontinued

) VALUES (

@MyProductName, @MySupplierID, @MyCategoryID, @MyQuantityPerUnit, @MyUnitPrice, @MyUnitsInStock, @MyUnitsOnOrder, @MyReorderLevel,

@MyDiscontinued

)

use the @@IDENTITY function to get the last inserted

identity value, which in this case is the ProductID of

the new row in the Products table

SET @ProductID = @@IDENTITY

return the ProductID

RETURN @ProductID

You can also create procedures using Enterprise Manager You do this by clicking the right mouse, button on the Stored Procedures node in the Databases folder and selecting New Stored Procedure You can then cut and paste the contents of AddProduct.sql into the Enterprise Manager properties dialog box, as shown in Figure 4.7 You'll notice I've added some comments to the start of the file that indicate what the procedure does

Figure 4.7: Using Enterprise Manager to define a procedure

You can view and modify a procedure by double-clicking the procedure name in

Enterprise Manager You can also delete a procedure using Enterprise Manager The Object Browser of Query Analyzer allows you to view, modify, and delete procedures as well

Tip You can also delete a procedure using the DROP PROCEDURE statement, and you can modify a procedure using the ALTER PROCEDURE statement

In the next section, you'll see how to run a stored procedure

Running a Stored Procedure

You run a procedure using the EXECUTE statement For example, the following

statements run the AddProduct() procedure:

DECLARE @MyProductID int

EXECUTE @MyProductID = AddProduct 'Widget', 1, 1, '1 Per box', 5.99, 10, 5, 5, 1 PRINT @MyProductID

With the initial set of rows in the Products table, the next identity value generated by SQL Server for the ProductID is 78, which is the value displayed by the previous

example if you run it

You can of course also pass variables as parameters to a procedure The following

example displays 79-the next ProductID:

DECLARE @MyProductID int

DECLARE @MyProductName nvarchar(40)

DECLARE @MySupplierID int

DECLARE @MyCategoryID int

DECLARE @MyQuantityPerUnit nvarchar(20)

DECLARE @MyUnitPrice money

DECLARE @MyUnitsInStock smallint

DECLARE @MyUnitsOnOrder smallint

DECLARE @MyReorderLevel smallint

DECLARE @MyDiscontinued bit

SET @MyProductName = 'Wheel'

SET @MySupplierID = 2

SET @MyCategoryID = 1

SET @MyQuantityPerUnit = '4 per box'

SET @MyUnitPrice = 99.99

SET @MyUnitsInStock = 10

SET @MyUnitsOnOrder = 5

SET @MyReorderLevel = 5

SET @MyDiscontinued = 0

EXECUTE @MyProductID = AddProduct @MyProductName, @MySupplierID, @MyCategoryID, @MyQuantityPerUnit, @MyUnitPrice, @MyUnitsInStock, @MyUnitsOnOrder, @MyReorderLevel, @MyDiscontinued

PRINT @MyProductID