Questions?

SQL Server Specialist Certificate Program

Maintaining SQL Server 2005

Week 4 – Creating Stored Procedures, Functions, and Triggers

Steve Stedman - Instructor

This Weeks Overview

● Review from Last Week + Homework● Class Project● Stored Procedures● Functions● System Stored Procedures● Triggers

● Review and Homework

Topics from last week

● Creating Tables● Implementing Constraints● XML

Homework

● Practice● Assignment● Reading

Class Project

● Status Update● Review of research and

experimentation required for the group project.

● Presentations will be week 9

Finding more Information

● When searching Google, search for ○ SQL Server 2005 _____○ TSQL _____

● This will help filter out other databases or sql languages.

● End of this section. Any Questions?

Preparation

We will be using the database created in week 3 for projects in class.We will also be using the AdventureWorks database.

1.Stored Procedures

● What are stored procedures?● What do you need to get started?● Writing your first stored procedure● Passing Parameters to stored

procedures● Output from stored procedures● Stored procedures in the SSMS UI

What are stored procedures?

● A name associated with a batch of SQL code, stored on the server

● Most-used programmatic structures in the database

● TSQL code is parsed once, and run many times for Stored Procedures.

What do you need to get started?

● Know what it is that you want to do in the procedure

● Know what the parameters are (if any)

● Know what needs to be returned● Figure out how to make it all work

Writing your first stored procedure

● A simple stored procedure can be created similar to how we created Views, first create a select statement, then save it as a procedure

CREATE PROCEDURE nameAS ● SELECT statement……

Sample Stored Procedure - Create

USE AdventureWorks; GO CREATE PROCEDURE Person.sp_who AS SELECT FirstName, LastName FROM Person.Contact;

Sample Stored Procedure - Execute

USE AdventureWorks; GO EXEC sp_who; EXEC Person.sp_who;

Sample Stored Procedure - Drop

USE AdventureWorks; GO DROP PROCEDURE Person.sp_who;

Passing Parameters to Stored Procedures

CREATE PROCEDURE spNewValue @pPKValue int, @pStatus char(8) AS

INSERT into MyTableSELECT Field1, Field2, 'Active' as StatusFrom MyTableWhere PKValue = @pPKValue

UPDATE MyTableSET Status = @pStatusWHERE PKValue = @pPKValue

Output from Stored Procedures

CREATE PROCEDURE [dbo].[uspLogError] @ErrorLogID [int] = 0 OUTPUTAS …BEGIN

SET @ErrorLogID = 7END

Stored Procedures in the SSMS UI

● Programmability..Stored Procedures● Look for

○ [HumanResources].[uspUpdateEmployeeLogin]

● Notice Try…Catch in stored procedure

Lab Project – Stored Procedures

● Create a stored procedure to wrap a SELECT statement

● Pass Data to the WHERE clause of a SELECT Stored Procedure

● Create a stored procedure to perform an insert statement using parameters

● Use the Week3 database or AdventureWorks

● End of this section. Any Questions?

1.Functions

● UDF = User Defined Functions

● Scalar Functions● Table Value / Rowset Functions● Deterministic / Non Deterministic● Built In Functions● Functions in the SSMS UI

Scalar Functions

● Accept 0 or more parameters● Return a single value● Similar to a simple function in most

any programming language

Table Value / Rowset Functions

● Similar to scalar, but return a table set

● Needs to have a table defined as the output

● See page 354-356

Deterministic / Non Deterministic

● Non Deterministic○ Different output given same input.○ Example Age_in_Seconds(‘7/21/1942’)

● Deterministic○ Returns same output for a given input

every time○ Can be indexed / clustered in a view

Built In Functions

● GETDATE()● DATEDIFF (datepart, startdate,

enddate ) ● SUBSTRING(value, start, length)● LEN(string_expression)● LOWER(string_expression)● @@SERVERNAME

Functions in the SSMS UI

● Programmability..Functions● Look for

○ [dbo].[ufnLeadingZeros]

● Notice RETURN (@ReturnValue);● SCHEMABINDING – improved

performance – prevents alter or drop on referenced tables and columns

Lab Project –

● Create a Scalar Function● Create a Table Value Function

● Run both execute both of these functions in the query editor

● End of this section. Any Questions?

● 10 Minute Break

3. System Stored Procedures● Administrative and informational activities

can be performed by using system stored procedures

● Example of sp_help on AdventureWorks○ EXEC sp_help '[Production].

[ProductProductPhoto]';

Lab Project

Use sp_help on the Week3 or AdventureWorks databases to find out information about one or more tables

Example: EXEC sp_help '[Production].[ProductProductPhoto]';

● End of this section. Any Questions?

4. Triggers

● Triggers Overview● DML triggers● After and Instead Of triggers● DDL triggers● Recursive and Nested triggers● Common uses of triggers

Triggers Overview

● Triggers are “Fired” on a specific event

● A useful addition to constraints● Data can be validated● See [AdventureWorks].[ddlDatabaseTriggerLog]

● Can cause code to be executed that may not be expected

● Show up in the query optimizer

DML triggers

● Attached to a specific table or view● Useful to track changes or log changes● See [HumanResources].[uDepartment]● INSERT and UPDATE

○ Could be used to update a “Last updated” column in the table

● DELETE○ Could be used to delete FK relations after the

row is deleted

After and Instead of Triggers

● AFTER triggers○ Run after the action is completed○ Default if INSTEAD of is not specified

● INSTEAD OF triggers○ Run instead of the action○ Useful for views – allows inserting to a

view

DML triggers example

CREATE TRIGGER [HumanResources].[dEmployee] ON [HumanResources].[Employee] INSTEAD OF DELETE AS BEGINSET NOCOUNT ON;DECLARE @DeleteCount int;SELECT @DeleteCount = COUNT(*) FROM deleted;IF @DeleteCount > 0 BEGINRAISERROR (N'Employees cannot be deleted. They can only be marked as not current.', 10, 1); -- Rollback any active or uncommittable transactionsIF @@TRANCOUNT > 0BEGINROLLBACK TRANSACTION;ENDEND;END;

DDL triggers

● Used to audit and regulate actions performed on the database

● Triggered on:○ Table creation, modification or drop○ Users are added (login added) or

dropped○ Databases created or dropped

DDL triggers example

Create TRIGGER trig_event_data ON DATABASE FOR CREATE_TABLE AS PRINT 'CREATE TABLE Issued.'select eventdata()RAISERROR ('New tables cannot be created in this database.', 16, 1) ROLLBACK;

Recursive and Nested triggers

● A trigger causing itself to fire is called recursion

● A trigger which modifies another table and causes a trigger to fire is called nested

● INSTEAD OF triggers do not fire recursively

● You can disable nested triggers at the server level

Common uses of triggers

● Enforce business rules● Validate input data● Write to other tables for audit trail

purposes● Query from other tables for cross-

referencing purposes● Access system functions (for example, print

an exception message when a rule is violated)

● Replicate data to different tables to achieve data consistency

Lab Project

● Using the AdventureWorks or Week3 databases:○ Create a DML trigger to prevent deleting

of a row in a table○ Create a DDL trigger to prevent the

creation of a table○ Create a DML trigger to convert a

varchar column to all caps (Use the UPPER function)

● End of this section. Any Questions?

Homework

● Homework for next week○ Handout