Copyright © Curt Hill Stored Procedures In Transact-SQL

Introduction In a previous presentation we examined the programming features of SQL Server’s extensions to SQL What we did not cover are Procedures or Functions –Important aspects of real programming Today we fix that First, how to executed Second, a sampling of predefined stored procedures Third, how to define Copyright © Curt Hill

Executing a procedure A stored procedure is started by the Execute statement –Which may be abbreviated to Exec The format is: EXEC[UTE] = ] spname [ parms ] –Where –Spname is the name of procedure –The return value is optional and placed in a previously declared variable –The parameters vary per procedure Copyright © Curt Hill

Notes The parameters may be defined by name or positionally To define by name = value The values passed to a stored procedure may be constants, variables or table values Next we will survey a few predefined stored procedures and then look at some example calls Copyright © Curt Hill

Some predefined Predefined stored procedures have a common naming convention –Always starts with sp_ or xp_ There are more than 350 predefined ones –Just a few of these will be examined Copyright © Curt Hill

List 1 sp_add_job – adds a batch job to the system See also sp_add_jobstep and sp_add_jobschedule, sp_update_job, etc. sp_addlogin – add a login name and password sp_addmessage – add an error message to system error message table sp_catalogs – displays catalog listing Copyright © Curt Hill

List 2 sp_columns – display catalog info for tables or views sp_databases – display the databases on this server sp_executesql – execute a statement within a string sp_help – display help – many others such as sp_helpindex sp_indexes – display index information Copyright © Curt Hill

List 3 sp_lock – displays information in locks sp_monitor – displays information on resources sp_password – update the password for a login sp_primarykeys – duh sp_rename sp_tables Copyright © Curt Hill

Execute examples Copyright © Curt Hill

The other prefix There are a series of stored procedures that start with xp_ These are typically system commands, rather than database commands An example is: xp_cmdshell ‘cmd’ The cmd is passed to windows to be executed Copyright © Curt Hill

Defining our own We may also define our own stored procedures A stored procedure is just that: Transact SQL code that is stored on the server It may then be used just like a predefined The Create Procedure command creates and stores it on the server Copyright © Curt Hill

Create Procedure Form: CREATE PROC[EDURE] procedure_name [;number] parms as statements Where –Procedure_name is the name –Number is optional and creates a group of procedures –Parms is discussed next –Statements are the body of the procedure Copyright © Curt Hill

Parameters There are zero or more parameters The type [VARYING] [= value] [OUTPUT] The name is first, followed by the type Varying is only used if this is a cursor type Output means that the parameter is a reference type The = gives a default value Copyright © Curt Hill

Notes The parameter must follow the normal naming convention –Start if normal variable –Start with letter if cursor Cursors must use varying and output Copyright © Curt Hill

Connection Stored procedures belong to a particular database Therefore the use is almost always required However, Create Procedure must be the first command in a batch Thus separate with a GO Copyright © Curt Hill

Example 1 A stored procedure that does a simple query: Create Procedure MyProc AS Select f_name, f_naid From faculty Where f_age > 40 Stored procedures are precompiled, so executing this is faster than the normal query Copyright © Curt Hill

Return value A stored procedure may return an integer only It does this with the return statement The form of the execute then becomes: = Proc parms Copyright © Curt Hill

Count Rows Here is an example that will count rows in this query –This could be done easily with an aggregate function but this is a nice example There are two pieces –The stored procedure –The use of it Copyright © Curt Hill

Counter Definition Copyright © Curt Hill use college go Create Proc Counter as return varchar(20) = 0 declare curses Cursor for select f_name from faculty where f_age > 40 open curses fetch next from curses while >= 0) begin + 1 fetch next from curses end deallocate

Counter Use Copyright © Curt Hill use college int = -11 = Counter Results in no table output but only this in messages 14

Output values If the procedure needs to produce something other than one integer, then reference parameters are needed These have OUTPUT as a suffix on the parameter declaration They also need these in the actual parameter list What does this tell us about Microsoft designed languages? Copyright © Curt Hill

Last Example Lets find the highest and lowest ratios again The stored procedure is simliar to the version in the Transact SQL presentation Only the prefix is different Copyright © Curt Hill

High Low Defined Copyright © Curt Hill use college go create proc real varchar(20) real varchar(20) output as declare fac_curse cursor for select f_name, f_age, f_years from faculty where f_age > 40 open fac_curse -- Rest is same

High Low Called Copyright © Curt Hill use college varchar(20) exec output print 'Lowest + ' ' + print 'Highest + ' ' +

Execute again The normal purpose of the Execute command is to start a stored procedure It has another use as well It may execute a string –Literal –Variable The string should be a query or other executable command Copyright © Curt Hill

Notes The string option allows us to pass a query or other command to a stored procedure This will mess with optimization Normally a stored procedure is precompiled –However it cannot precompile a command it has not received Copyright © Curt Hill

Other procedure commands We remove procedures with: DROP PROCEDURE proc_name This must be executed within the correct database We may also Alter the stored procedure Copyright © Curt Hill

Functions A function is a procedure that returns a value The syntax is similar: Create Function name type, … ) Returns type Begin body Return expression End Copyright © Curt Hill

There is More SQL Server has no monopoly on these things Oracle, MySQL, PostgreSQL, DB2 among others, have both procedures and functions There should be no surprise that –The capabilities are similar –The syntax is different Copyright © Curt Hill

Finally A stored procedure saves us work for frequently used code It is faster than the normal because it is precompiled It may also be used by anyone on the database Copyright © Curt Hill