Stored Procedures

CIS-182

BATCH

• Batch is a logical group of SQL statements– Run-time error will halt execution only of

FURTHER steps– Can break up work

• Stored procedures• User-defined functions• Views

Scripts v. Stored Procedures

• Script: Text file of SQL commands• Stored Procedure: SQL commands stored

in database itself– SPROC’s have more capabilities than a script

Format of SPROC’s

CREATE PROC <name> <parameter list>

AS<instructions to execute>

EXECUTE

• EXEC(cute) statementOR

• EXEC(cute) stored procedure name• Statement or sproc runs in it’s own scope– Can’t ‘share’ variables directly– User’s security rules apply– Can’t be used in User Defined Function (UDF)

Uses of Stored Procedures

• For returning data • For editing data• For calculations

Parameters

• Method for sending data into and from a stored procedure– INPUT parameters are values sent in– OUTPUT parameters are values returned

• Must have a holding space (variable) for the returned data

• Defined before start of procedure (AS)

Declaring Parameters

• Include name and datatype• Default value is optional– Without a default value, parameter is required

• Direction is optional (input is default)– An output parameter must have direction

specified

Sample Input Parameter

CREATE PROC upFindStudent@SID char(9)

ASSELECT *

FROM Students_TWhere SchoolID=@SID

Sample Output Parameter

CREATE PROC upFindStudentID@First varchar(25),@Last varchar(35),@SID char(9) OUTPUT

ASSELECT @SID=SchoolID

FROM Students_T

Where @First=Firstname and @Last=Lastname

Variables

• Create using DECLARE• Need to start with ‘@’• Can use SQL data types or custom data

types

DECLARE @StudentName varchar(50)

Variable Assignment

• SET is usually used similar to procedural languageSET @Var=value

• SELECT is usually used when getting a value from a querySELECT @Var=Sum(PossiblePoints) FROM

Assignments

Return Values

• Result of stored procedure indicates success or failure

• Non-zero value indicates a problem• Must be an integer• Different from an output parameter– Output parameter is about data

• RETURN <value>– Causes immediate exit

Decision-making

• IF … ELSE– No end if– Need to use Begin/End if have more than one

instruction to executeIF StartDate < EndDate

Begin…End

ELSE

Simple Case Statement

• CASE– Similar to SELECT CASE or SWITCH– Compares one value to different cases

CASE Category

WHEN ‘pop_comp’ THEN ‘Popular Computing’

WHEN ‘mod_cook’ THEN ‘Modern Cooking’

END

Searched CASE

• No test expression• Each WHEN has a boolean test

CASEWHEN Points >= 90 THEN ‘A’WHEN Points < 90 AND Extra > 0

THEN ‘A’

END

@@Error – System Variable

• Determined after each SQL statement;• 0 means statement was successful• Number other than zero is typically a

specific error• Can store value in variable and test

@@Identity – System Variable

• Returns the last identity value used as a result of INSERT or SELECT INTO

• Returns Null if operation failed or a value wasn’t generated

• Returns last number created if multiple inserts occur (i.e. SELECT INTO)

@@Rowcount – System Variables

• Number of rows returned or affected by the last statement

• 0 (zero) is often used as a logical test– If no records found for where clause, notify

system or process