Microsoft SQL Server 2008 R2 Unleashed- P96 potx

ptg 894 CHAPTER 28 Creating and Managing Stored Procedures Processing goes here RETURN If you want to help identify the data values for which the parameters are defined, it is recommended that you give your parameters meaningful names. Parameter names, like local variables, can be up to 128 characters in length, including the @ sign, and they must follow SQL Server rules for identifiers. Up to 2,100 parameters can be defined for a stored procedure. When you execute a procedure, you can pass the parameters by position or by name: Passing parameters by position EXEC myproc 1, 2, 3 Passing parameters by name EXEC myproc @parm2 = 2, @parm2 = 1, @parm3 =3 Passing parameters by position and name EXEC myproc 1, @parm3 =3, @parm2 = 2 After you specify one parameter by name, you must pass all subsequent parameters for the procedure in that EXECUTE statement by name as well. You cannot pass any of the subse- quent parameters by position. If you want to skip parameters that are not the last parame- ter(s) in the procedure and have them take default values (as described in the next section), you also need to pass parameters by name or use the DEFAULT keyword in place of the parameter value. TIP When you are embedding calls to stored procedures in client applications and script files, it is advisable to pass parameters by name. Reviewing and debugging the code becomes easier that way. One time we spent half a day debugging a set of nested stored procedures to figure out why they weren’t working correctly, only to find the problem was due to a missed parameter; all the parameter values were shifted over one place and the wrong values ended up being passed to the wrong parameters. This resulted in the queries not finding any matching values. Had the parameters been passed by name, this issue would not have occurred. This was a lesson learned the hard way! Input parameter values passed in can be only explicit constant values, local variables, parameters, or, new for SQL Server 2008, table-valued parameters. However, you cannot specify a function or another expression as an input parameter value. You would have to store a return value from the function or expression value in a local variable and pass the local variable as the input parameter. Likewise, you cannot use a function or another expression as a default value for a parameter. Download from www.wowebook.com ptg 895 Using Input Parameters 28 Setting Default Values for Parameters You can assign a default value to a parameter by specifying a value in the definition of the parameter, as shown in Listing 28.11. LISTING 28.11 Assigning a Default Value for a Parameter in a Stored Procedure ALTER PROCEDURE title_authors @state char(2) = ‘%’ AS 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 WHERE a.state like @state RETURN GO You can have SQL Ser ver apply the default value for a parameter during execution by not specifying a value or by specifying the DEFAULT keyword in the position of the parameter, as shown in Listing 28.12. LISTING 28.12 Applying a Default Value for a Parameter When Executing a Stored Procedure EXEC title_authors EXEC title_authors DEFAULT EXEC title_authors @state = DEFAULT TIP If you are involved in creating stored procedures that other people will use, you proba- bly want to make the stored procedures as easy to use as possible. If you leave out a parameter that is required, SQL Server presents an error message. The myproc procedure, shown earlier in this section, requires three parameters: @parm1, @parm2, and @parm3: EXEC myproc Server: Msg 201, Level 16, State 4, Procedure myproc, Line 0 Procedure ‘myproc’ expects parameter ‘@parm1’, which was not supplied. Note that SQL Server complains only about the first missing parameter. The program- mer passes the first parameter, only to find out that more parameters are required. This is a good way to annoy a programmer or an end user. Download from www.wowebook.com ptg 896 CHAPTER 28 Creating and Managing Stored Procedures When you execute a command-line program, you probably expect that you can use /? to obtain a list of the parameters the program expects. You can program stored proce- dures in a similar manner by assigning NULL (or some other special value) as a default value to the parameters and checking for that value inside the procedure. The following is an outline of a stored procedure that presents the user with information about the parameters expected if the user doesn’t pass parameters: CREATE PROC MyProc2 @parm1 int = NULL, @parm2 int = 32, @parm3 int = NULL AS IF (@parm1 IS NULL or @parm1 NOT BETWEEN 1 and 10) OR @parm3 IS NULL PRINT ‘Usage: EXEC MyProc2 @parm1 int, (Required: Can be between 1 and 10) @parm2 = 32, (Optional: Default value of 32) @parm3 int, (Required: Any number within range)’ Processing goes here RETURN GO EXEC MyProc2 GO Usage: EXEC MyProc2 @parm1 int, (Required: Can be between 1 and 10) @parm2 = 32, (Optional: Default value of 32) @parm3 int, (Required: Any number within range) You can develop your own standar ds for t he way t he message is presented to the user, but what is important is that the information is presented at all. To display the parameters defined for a stored procedure, you can view them in the SSMS Object Explorer (see Figure 28.7) or by executing the sp_help stored procedure, as shown in Listing 28.13. (Note that the output has been edited to fit the page.) LISTING 28.13 Displaying Stored Procedure Parameters by Using sp_help exec sp_help title_authors Name Owner Type Created_datetime Download from www.wowebook.com ptg 897 Using Input Parameters 28 FIGURE 28.7 Displaying stored procedure parameters in SSMS. title_authors dbo stored procedure 2008-09-15 21:15:06.540 Parameter_name Type Length Prec Scale Param_order Collation @state char 2 2 NULL 1 SQL_Latin1_General_CP1_CI_AS You can also display the stored procedure parameters by running a query against the INFORMATION_SCHEMA view parameters: select substring(Parameter_NAME,1, 30) as Parameter_name, substring (DATA_TYPE, 1, 20) as Data_Type, CHARACTER_MAXIMUM_LENGTH as Length, ordinal_position as param_order, Collation_name from INFORMATION_SCHEMA.parameters where specific_name = ‘title_authors’ and specific_schema = ‘dbo’ order by ordinal_position go Download from www.wowebook.com ptg 898 CHAPTER 28 Creating and Managing Stored Procedures Parameter_name Data_Type Length param_order Collation_name @state char 2 1 SQL_Latin1_General_CP1_CI_AS You can view parameter information for a stored procedure as well using the sys.parameters catalog view: select substring(p.name,1, 30) as Parameter_name, substring (t.name, 1, 20) as Data_Type, p.max_length as Length, parameter_id as param_order, default_value from sys.parameters p inner join sys.types t on p.user_type_id = t.user_type_id where p.object_id = object_id(‘title_authors’) order by parameter_id go Parameter_name Data_Type Length param_order default_value @state char 2 1 NULL Passing Object Names as Parameters In SQL Server 2008, if you pass an object name as a parameter to a stored procedure, SQL Server attempts to treat it as a table-valued parameter unless the object name is used either as an argument in a WHERE clause or in a dynamic SQL query. For example, the code in Listing 28.14 generates an error message when you try to create the stored procedure. LISTING 28.14 Attempting to Create a Stored Procedure by Using a Parameter to Pass in a Table Name CREATE proc find_data @table varchar(128) as select * from @table GO Msg 1087, Level 16, State 1, Procedure find_data, Line 4 Must declare the table variable “@table”. As you can see, when the parameter is used in the FROM clause, SQL Server expects it to be defined as a table variable. To use the value in the parameter as a table name, you can build a dynamic SQL query similar to the example shown in Listing 28.15. Download from www.wowebook.com ptg 899 Using Input Parameters 28 LISTING 28.15 Passing a Table as a Parameter to a Stored Procedure for Dynamic SQL Execution CREATE proc find_data @table varchar(128) as exec (‘select * from ‘ + @table) return go exec find_data @table = ‘publishers’ go pub_id pub_name city state country 0736 New Moon Books Boston MA USA 0877 Binnet & Hardley Washington DC USA 1389 Algodata Infosystems Berkeley CA USA 1622 Five Lakes Publishing Chicago IL USA 1756 Ramona Publishers Dallas TX USA 9952 Scootney Books New York NY USA 9999 Lucerne Publishing Paris NULL France Using Wildcards in Parameters Wildcards can be included in varchar-based input parameters and used in a LIKE clause in a query to perform pattern matching. However, you should not use the char data type for parameters that will contain wildcard characters because SQL Server pads spaces onto the value passed in to the parameter to expand it to the specified size of the char data type. For example, if you declared an @lastname parameter as char(40) and passed in ’S%’, SQL Server would search not for a string starting with ’S’ but for a string starting with ’S’, any characters, and ending with up to 38 spaces. This would likely not match any actual data values. Also, to increase the flexibility of a stored procedure that searches for character strings, you can default the parameter to ’%’, as in the following example: IF EXISTS ( SELECT * FROM sys.procedures WHERE schema_id = schema_id(‘dbo’) AND name = N’find_authors’) DROP PROCEDURE dbo.find_authors GO create proc find_authors @lastname varchar(40) = ‘%’ as select au_id, au_lname, au_fname Download from www.wowebook.com ptg 900 CHAPTER 28 Creating and Managing Stored Procedures from authors where au_lname like @lastname order by au_lname, au_fname This procedure, if passed no parameter, returns data for all authors in the authors table. If passed a string containing wildcard characters, this procedure returns data for all authors matching the search pattern specified. If a string containing no wildcards is passed, the query performs a search for exact matches against the string value. Unfortunately, wildcard searches can be performed only against character strings. If you want to have similar flexibility searching against a numeric value, such as an integer, you can default the value to NULL and when the parameter is NULL, compare the column with itself, as shown in the following example: IF EXISTS ( SELECT * FROM sys.procedures WHERE schema_id = schema_id(‘dbo’) AND name = N’find_titles_by_sales’) DROP PROCEDURE dbo.find_titles_by_sales GO create proc find_titles_by_sales @ytd_sales int = null as select title_id, title, ytd_sales from titles where ytd_sales = isnull(@ytd_sales, ytd_sales) However, the problem with this approach is that the procedure returns all rows from the titles table except those in which ytd_sales contains a NULL value. The reason is that NULL is never considered equal to NULL; you cannot compare an unknown value with another unknown value. To return all rows, including those in which ytd_sales is NULL, you need to implement a dual-query solution, as in the following example: IF EXISTS ( SELECT * FROM sys.procedures WHERE schema_id = schema_id(‘dbo’) AND name = N’find_titles_by_sales’) DROP PROCEDURE dbo.find_titles_by_sales GO create proc find_titles_by_sales @ytd_sales int = null as if @ytd_sales is null select title_id, title, ytd_sales from titles else select title_id, title, ytd_sales from titles where ytd_sales= @ytd_sales Download from www.wowebook.com ptg 901 Using Input Parameters 28 Using Table-Valued Parameters In previous versions of SQL Server, it was not possible to share the contents of table vari- ables between stored procedures. SQL Server 2008 changes that with the introduction of table-valued parameters, which allow you to pass table variables to stored procedures. Table-valued parameters provide more flexibility and, in many cases, better performance than temporary tables as a means to pass result sets between stored procedures. NOTE For more information on using temporary tables and the table data type in stored pro- cedures, see Chapter 44. Table-valued parameters provide many of the same performance advantages as table data types. Table-valued parameters also share some of the same restrictions as table variables, such as SQL Server not maintaining statistics on table-valued parameters and table-valued parameters not permitted as the target of a SELECT INTO or INSERT EXEC statement. In addition, table-valued parameters can be passed only as READONLY input parameters to stored procedures. DML operations, such as UPDATE, INSERT, and DELETE, cannot be performed on table-valued parameters within the body of a stored procedure. To create and use table-valued parameters, you must first create a user-defined table type and define the table structure. You do so using the CREATE TYPE command, as in the following example: if exists (select * from sys.systypes t where t.name = ‘ytdsales_tabletype’ and t.uid = USER_ID(‘dbo’)) drop type ytdsales_tabletype go CREATE TYPE ytdsales_tabletype AS TABLE (title_id char(6), title varchar(50), pubdate date, ytd_sales int) go After the table data type is created, you can use it for declaring local table variables and for stored procedure parameters. To use the table-valued parameter in a procedure, you create a procedure to receive and access data through a table-valued parameter: /* Create a procedure to receive data for the table-valued parameter. */ if OBJECT_ID(‘tab_parm_test’) is not null drop proc tab_parm_test go create proc tab_parm_test Download from www.wowebook.com ptg 902 CHAPTER 28 Creating and Managing Stored Procedures @pubdate datetime = null, @sales_minimum int = 0, @ytd_sales_tab ytdsales_tabletype READONLY as set nocount on if @pubdate is null if no date is specified, set date to last year set @pubdate = dateadd(month, -12, getdate()) select * from @ytd_sales_tab where pubdate > @pubdate and ytd_sales >= @sales_minimum return go Then, when calling that stored procedure, you declare a local table variable using the table data type defined previously, populate the table variable with data, and then pass the table variable to the stored procedure: /* Declare a variable that references the type. */ declare @ytd_sales_tab ytdsales_tabletype /* Add data to the table variable. */ insert @ytd_sales_tab select title_id, convert(varchar(50), title), pubdate, ytd_sales from titles /* Pass the table variable populated with data to a stored procedure. */ exec tab_parm_test ‘6/1/2001’, 10000, @ytd_sales_tab go title_id title ytd_sales BU2075 You Can Combat Computer Stress! 18722 MC3021 The Gourmet Microwave 22246 TC4203 Fifty Years in Buckingham Palace Kitchens 15096 Using Output Parameters If a calling batch passes a variable as a parameter to a stored procedure and that parameter is modified inside the procedure, the modifications are not passed to the calling batch unless you specify the OUTPUT keyword for the parameter when executing the stored proce- dure. Download from www.wowebook.com ptg 903 Using Output Parameters 28 If you want a procedure to be able to pass parameter values out from the procedure, you need to use the keyword OUTPUT when creating the procedure. The following example shows a stored procedure that accepts two parameters, one of which is used as an output parameter: IF EXISTS ( SELECT * FROM sys.procedures WHERE schema_id = schema_id(‘dbo’) AND name = N’ytd_sales’) DROP PROCEDURE dbo.ytd_sales GO CREATE PROC ytd_sales @title varchar(80), @ytd_sales int OUTPUT AS SELECT @ytd_sales = ytd_sales FROM titles WHERE title = @title RETURN The calling batch (or stored procedure) needs to declare a variable to store the returned value. The execute statement must include the OUTPUT keyword as well, or the modifications won’t be reflected in the calling batch’s variable: DECLARE @sales_up_to_today int EXEC ytd_sales ‘Life Without Fear’, @sales_up_to_today OUTPUT PRINT ‘Sales this year until today’’s date: ‘ + CONVERT(VARCHAR(10), @sales_up_to_today) + ‘.’ Sales this year until today’s date: 111. You can also pass the output parameter by name: DECLARE @sales_up_to_today int EXEC ytd_sales ‘Life Without Fear’, @ytd_sales = @sales_up_to_today OUTPUT PRINT ‘Sales this year until today’’s date: ‘ + CONVERT(VARCHAR(10), @sales_up_to_today) + ‘.’ Note that when you pass an output parameter by name, the parameter name (@ytd_sales, in this example) is listed on the left side of the expression, and the local variable ( @sales_up_to_today), which is set equal to the value of the output parameter, is on the right side of the expression. An output parameter can also serve as an input parameter. Output parameters can also be passed back and captured in a client application by using ADO, ODBC, OLE DB, and so on. Download from www.wowebook.com . char 2 1 NULL Passing Object Names as Parameters In SQL Server 2008, if you pass an object name as a parameter to a stored procedure, SQL Server attempts to treat it as a table-valued parameter. Table-Valued Parameters In previous versions of SQL Server, it was not possible to share the contents of table vari- ables between stored procedures. SQL Server 2008 changes that with the introduction. passed in can be only explicit constant values, local variables, parameters, or, new for SQL Server 2008, table-valued parameters. However, you cannot specify a function or another expression