Microsoft SQL Server 2008 R2 Unleashed- P104 ppt

CHAPTER 30 Creating and Managing Triggers --update the data related to the jobs table UPDATE jobs SET jobs.min_lvl = i.min_lvl, jobs.max_lvl = i.max_lvl, jobs.job_desc = i.job_desc FROM

CHAPTER 30 Creating and Managing Triggers

update the data related to the jobs table

UPDATE jobs

SET jobs.min_lvl = i.min_lvl,

jobs.max_lvl = i.max_lvl,

jobs.job_desc = i.job_desc

FROM inserted i

WHERE jobs.job_id = i.job_id

AND (jobs.min_lvl <> i.min_lvl

OR jobs.max_lvl <> i.max_lvl

OR jobs.job_desc <> i.job_desc)

update the data related to the employee table

UPDATE employee

SET employee.job_lvl = i.min_lvl

FROM inserted i

WHERE employee.emp_id = i.emp_id

GO

A section in Listing 30.13 checks the fields related to the jobs table and updates the base

table if any of the values have changed Another section updates the employee table for

the employee fields that have been changed in the view

NOTE

You could enhance the trigger in Listing 30.13 to include logic to check for specific

updates or to update only those employees who are assigned to the job and have a job

level below the new minimum These enhancements are not included in the listing to

keep the example simple

If you now execute the same UPDATE statement, you don’t get an error message:

UPDATE employeeJobs

SET min_lvl = 40,

job_lvl = 40

WHERE job_id = 12

GO

The following results show values selected from the employeeJobs view after the update is

executed successfully:

min_lvl max_lvl job_id job_desc job_lvl emp_id

- - - -

-25 100 14 Designer 35 ENL44273F

25 100 14 Designer 89 PSA89086M

25 100 14 Designer 100 KFJ64308F

25 100 13 Sales Representative 35 PMA42628M

25 100 13 Sales Representative 64 CGS88322F

25 100 13 Sales Representative 100 TPO55093M

40 100 12 Editor 40 Y-L77953M

40 100 12 Editor 40 H-B39728F

40 100 12 Editor 40 HAS54740M

Notice that the Editor job now has a minimum level (min_lvl) equal to 40 and that all

the employees who have that job level (job_lvl) are also set to 40

You can see the added flexibility that you get by using the INSTEAD OF trigger on a basic

view This flexibility is also applicable to a more sophisticated view called a distributed

partitioned view With this type of view, data for the view can be partitioned across

differ-ent servers Partitioning this way enables you to scale a database solution and still have a

single view of the data that appears as one table

You can make data modifications via a distributed partitioned view, but some restrictions

exist If you do not meet the requirements for updating the view, you can use the INSTEAD

OF trigger to bypass these restrictions; this is similar to adding an INSTEAD OF trigger on a

nonpartitioned view

INSTEAD OF Trigger Restrictions

INSTEAD OF triggers have many capabilities, but they also have limitations Following are

some of them:

INSTEAD OF triggers do not support recursion This means they cannot call

them-selves, regardless of the setting of the Recursive Triggers database option For

example, if an INSERT is executed on a table that has an INSTEAD OF trigger, and the

INSTEAD OF trigger performs an INSERT on this same table, the INSTEAD OF trigger for

this INSERT does not fire a second time Any AFTER triggers defined on the same

table for INSERT fire based on the INSTEAD OF trigger INSERT

You can define only one INSTEAD OF trigger for each action on a given table

Therefore, you can have a maximum of three INSTEAD OF triggers for each table: one

for INSERT, one for UPDATE, and one for DELETE

A table cannot have an INSTEAD OF trigger and a FOREIGN KEY constraint with CASCADE

defined for the same action For example, you cannot have an INSTEAD OF trigger

defined for DELETE on a given table as well as a foreign key with a CASCADE DELETE

definition You get an error if you attempt to do this In this situation, you could have

INSTEAD OF triggers defined on INSERT and UPDATE without receiving errors

CHAPTER 30 Creating and Managing Triggers

Using DDL Triggers

DDL triggers were introduced in SQL Server 2005 These triggers focus on changes to the

definition of database objects as opposed to changes to the actual data The definition of

database objects is dictated by the DDL events that these triggers respond to

The DDL events that these triggers fire on can be broken down into two main categories

The first category includes DDL events that are scoped at the database level and affect the

definition of objects such as tables, indexes, and users The second category of DDL

trig-gers is scoped at the server level These trigtrig-gers apply to server objects, such as logins

The number of DDL events at the database level far exceeds the number at the server

level Table 30.2 lists the DDL statements and system stored procedures that DDL triggers

can fire on

TABLE 30.2 DDL Statements and System Stored Procedures*

Create/Grant/Bind/Add Alter/Update/Deny Drop/Revoke/Unbind

Statements and System Stored Procedures with Database-Level Scope

CREATE_APPLICATION_ROLE ALTER_APPLICATION_ROLE DROP_APPLICATION_ROLE

(sp_addapprole) (sp_approlepassword) (sp_dropapprole)

ALTER_AUTHORIZATION_

DATABASE (sp_changedbowner) CREATE_CERTIFICATE ALTER_CERTIFICATE DROP_CERTIFICATE

CREATE_EXTENDED_PROPERTY ALTER_EXTENDED_PROPERTY DROP_EXTENDED_PROPERTY

(sp_addextendedproperty) (sp_updateextendedproperty) (sp_dropextended

property) CREATE_FULLTEXT_INDEX ALTER_FULLTEXT_INDEX

DROP_FULLTEXT_INDEX (sp_fulltexttable) ( sp_fulltextcatalog) (sp_fulltexttable)

TABLE 30.2 DDL Statements and System Stored Procedures*

Create/Grant/Bind/Add Alter/Update/Deny Drop/Revoke/Unbind

(sp_fulltext_column)

(sp_indexoption)

CREATE_MESSAGE_TYPE ALTER_MESSAGE_TYPE DROP_MESSAGE_TYPE

CREATE_PARTITION_FUNCTION ALTER_PARTITION_FUNCTION DROP_PARTITION_FUNCTION

CREATE_PARTITION_SCHEME ALTER_PARTITION_SCHEME DROP_PARTITION_SCHEME

(sp_create_plan_guide) (sp_control_plan_guide) (sp_control_plan_guide)

CREATE_REMOTE_SERVICE_ ALTER_REMOTE_SERVICE_ DROP_REMOTE_SERVICE_

RENAME

(sp_rename)

(sp_addrole and

sp_addgroup)

(sp_droprole and sp_dropgroup) ADD_ROLE_MEMBER ALTER_ROUTEDROP_ROLE_MEMBER

(sp_addrole and sp_adduser) (sp_changeobjectowner)

(sp_addgroup and

sp_grantdbaccess)

CHAPTER 30 Creating and Managing Triggers

TABLE 30.2 DDL Statements and System Stored Procedures*

Create/Grant/Bind/Add Alter/Update/Deny Drop/Revoke/Unbind

CREATE_SYMMETRIC_KEY ALTER_SYMMETRIC_KEY DROP_SYMMETRIC_KEY

(sp_tableoption)

(sp_settriggerorder)

(sp_adduser and

sp_grantdbaccess)

(sp_change_users_login) (sp_dropuser and

sp_revokedbaccess)

CREATE_XML_SCHEMA_ ALTER_XML_SCHEMA_ DROP_XML_SCHEMA_

Statements and System Stored Procedures with Server-Level Scope

ALTER_AUTHORIZATION_

SERVER

(sp_fulltext_database) CREATE_ENDPOINT ALTER_ENDPOINTDROP_ENDPOINT

ALTER_INSTANCE

TABLE 30.2 DDL Statements and System Stored Procedures*

Create/Grant/Bind/Add Alter/Update/Deny Drop/Revoke/Unbind

(sp_configure and

sp_addserver)

CREATE_LINKED_SERVER ALTER_LINKED_SERVER DROP_LINKED_SERVER

(sp_addlinkedserver) (sp_serveroption) (sp_dropserver)

CREATE_LINKED_SERVER_

LOGIN

DROP_LINKED_SERVER_

LOGIN

(sp_addlogin and

sp_grantlogin)

(sp_defaultdb and sp_defaultlanguage)

(sp_droplogin and sp_revokelogin (xp_grantlogin and

sp_denylogin)

(sp_password, sp_change_users_login)

(xp_revokelogin)

(sp_addmessage) (sp_altermessage) (sp_dropmessage)

CREATE_REMOTE_SERVER ALTER_REMOTE_SERVER DROP_REMOTE_SERVER

(sp_addserver) (sp_setnetname) (sp_dropserver)

Statements and System Stored Procedures with Database-Level Scope

Create/Grant/Bind/Add Alter/Update/Deny Drop/Revoke/Unbind

CREATE_APPLICATION_ROLE ALTER_APPLICATION_ROLE DROP_APPLICATION_ROLE

(sp_addapprole) (sp_approlepassword) (sp_dropapprole)

ALTER_AUTHORIZATION_

DATABASE(sp_changedbowner) CREATE_CERTIFICATE ALTER_CERTIFICATE DROP_CERTIFICATE

CHAPTER 30 Creating and Managing Triggers

TABLE 30.2 DDL Statements and System Stored Procedures*

Create/Grant/Bind/Add Alter/Update/Deny Drop/Revoke/Unbind

CREATE_EXTENDED_

PROPERTY

ALTER_EXTENDED_PROPERTY DROP_EXTENDED_PROPERTY

(sp_addextendedproperty) (sp_updateextendedproperty) (sp_dropextendedproperty)

CREATE_FULLTEXT_INDEX ALTER_FULLTEXT_INDEX DROP_FULLTEXT_INDEX

(sp_fulltexttable) ( sp_fulltextcatalog) (sp_fulltexttable)

(sp_fulltext_column)

(sp_indexoption)

CREATE_MESSAGE_TYPE ALTER_MESSAGE_TYPE DROP_MESSAGE_TYPE

CREATE_PARTITION_FUNCTION ALTER_PARTITION_FUNCTION DROP_PARTITION_

FUNCTION CREATE_PARTITION_SCHEME ALTER_PARTITION_SCHEME DROP_PARTITION_SCHEME

(sp_create_plan_guide) (sp_control_plan_guide) (sp_control_plan_guide)

CREATE_REMOTE_SERVICE_BIN

DING

ALTER_REMOTE_SERVICE_BINDIN G

DROP_REMOTE_SERVICE_BIN DING

RENAME

(sp_rename)

(sp_addrole and

sp_addgroup)

(sp_droprole and sp_dropgroup)

TABLE 30.2 DDL Statements and System Stored Procedures*

Create/Grant/Bind/Add Alter/Update/Deny Drop/Revoke/Unbind

(sp_addrole and sp_adduser) (sp_changeobjectowner)

(sp_addgroup and

sp_grantdbaccess)

CREATE_SYMMETRIC_KEY ALTER_SYMMETRIC_KEY DROP_SYMMETRIC_KEY

(sp_tableoption)

(sp_settriggerorder)

(sp_adduser and

sp_grantdbaccess)

(sp_change_users_login) (sp_dropuser and

sp_revokedbaccess)

CREATE_XML_SCHEMA_

COLLECTION

ALTER_XML_SCHEMA_COLLECTION DROP_XML_SCHEMA_

COLLECTION

Statements and System Stored Procedures with Server-Level Scope

ALTER_AUTHORIZATION_

SERVER

CHAPTER 30 Creating and Managing Triggers

TABLE 30.2 DDL Statements and System Stored Procedures*

Create/Grant/Bind/Add Alter/Update/Deny Drop/Revoke/Unbind

(sp_fulltext_database)

ALTER_INSTANCE

(sp_configure and

sp_addserver)

CREATE_LINKED_SERVER ALTER_LINKED_SERVER DROP_LINKED_SERVER

(sp_addlinkedserver) (sp_serveroption) (sp_dropserver)

CREATE_LINKED_SERVER_

LOGIN

DROP_LINKED_SERVER_

LOGIN

(sp_addlogin and

sp_grantlogin)

(sp_defaultdb and sp_defaultlanguage)

(sp_droplogin and sp_revokelogin (xp_grantlogin and

sp_denylogin)

(sp_password, sp_change_users_login)

(xp_revokelogin)

(sp_addmessage) (sp_altermessage) (sp_dropmessage)

CREATE_REMOTE_SERVER ALTER_REMOTE_SERVER DROP_REMOTE_SERVER

(sp_addserver) (sp_setnetname) (sp_dropserver)

System stored procedures are enclosed in parentheses.

Triggers created on the DDL events are particularly important for auditing purposes In

the past, it was very difficult to isolate changes to the definition of a database or to

secure them from change With DDL triggers, you have the tools necessary to manage

these changes

Creating DDL Triggers

The basic syntax for creating a DDL trigger follows:

CREATE TRIGGER trigger_name

ON { ALL SERVER | DATABASE }

[ WITH <ddl_trigger_option> [ , n ] ]

{ FOR | AFTER } { event_type | event_group } [ , n ]

AS { sql_statement [ ; ] [ n ] | EXTERNAL NAME < method specifier > [ ; ] }

The best way to illustrate the use of the DDL trigger syntax and power of these triggers is

to look at a few examples The example shown in Listing 30.14 illustrates the creation of a

DDL trigger that is scoped at the database level and prevents table-level changes

LISTING 30.14 A Database-Scoped DDL Trigger for Tables

CREATE TRIGGER tr_TableAudit

ON DATABASE

FOR CREATE_TABLE, ALTER_TABLE, DROP_TABLE

AS

PRINT ‘You must disable the TableAudit trigger in order

to change any table in this database’

ROLLBACK

GO

This trigger is fired whenever the CREATE, ALTER, or DROP TABLE statements are executed

Consider, for example, the following statements that can be run against the

BigPubs2008 database:

ALTER table titles

add new_col int null

alter table titles

drop column new_col

You must disable the TableAudit trigger in order to change any table in this

database

Msg 3609, Level 16, State 2, Line 1

The transaction ended in the trigger The batch has been aborted

These ALTER statements add a column to the titles table and then remove the column

With the tr_TableAudit trigger in place on the BigPubs2008 database, the error message is

displayed after the first ALTER statement is executed