copyright © 2012-2013 - curt hill stored procedures in transact-sql

Copyright © 2012-2013 - 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


Executing a procedure• A stored procedure is started by the

Execute statement– Which may be abbreviated to Exec

• The format is:EXEC[UTE] [ @ret = ] 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


Notes

• The parameters may be defined by name or positionally

• To define by name use:@parm = 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


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


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


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


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


Execute examples


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


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


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


Parameters• There are zero or more parameters• The form:

@parm 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 valueCopyright © 2012-2013 - Curt Hill

Notes

• The parameter must follow the normal naming convention– Start with @ if normal variable– Start with letter if cursor

• Cursors must use varying and output


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


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


Return value

• A stored procedure may return an integer only

• It does this with the return statement

• The form of the execute then becomes:exec @var = Proc parms


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


Counter Definition


use collegegoCreate Proc Counter asreturn declare @count int, @name varchar(20) set @count = 0 declare curses Cursor for select f_name from faculty where f_age > 40 open curses fetch next from curses into @name while (@@FETCH_STATUS >= 0) begin set @count = @count + 1 fetch next from curses into @name end deallocate curses@count

Counter Use


use collegedeclare @acount intset @acount = -11exec @acount = Counter print @acount

Results in no table output but only this in messages14

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?


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


High Low Defined


use collegegocreate proc high_low @least_ratio real output, @least_name varchar(20) output, @most_ratio real output, @most_name varchar(20) output asdeclare fac_curse cursor for select f_name, f_age, f_years from faculty where f_age > 40open fac_curse -- Rest is same

High Low Called


use collegedeclare @lr real, @mr real, @ln varchar(20), @mn varchar(20)exec high_low @lr output, @ln output, @mr output, @mn outputprint 'Lowest '+@ln + ' ' + convert(varchar(20), @lr)print 'Highest '+@mn + ' ' + convert(varchar(20), @mr)

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


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


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


Functions• A function is a procedure that returns

a value• The syntax is similar:Create Function name (@parameter type, …)Returns typeBegin body Return expressionEnd


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


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 © 2012-2013 - curt hill stored procedures in transact-sql

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