Tài liệu Introducing Stored Procedures doc

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 . Introducing Stored Procedures SQL Server allows you to store procedures in a database. Stored procedures differ from user-defined functions in that procedures. @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