第 22 课PL/SQL5

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教学目标•Trigger•CREATE Trigger•MANAGE Trigger•使用 Trigger

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Overview of Triggers

• 触发器类似于函数和过程，它们都是具有声明部分、执行部分和异常处理部分的命名 P L / S Q L 块• 触发器是一个数据库对象，在数据库中以独立对象的身份存储• 触发器是在事件发生时隐式地运行的，并且触发器不能接收参数

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Overview of Triggers

• 触发事件可以是对数据库表的 D M L （ I N S E RT 、 U P D AT E 或 D E L E T E ）操作或某种视图的操作 ( Vi e w ) 。• Database triggers execute implicitly when an

DML statement (triggering statement) is issued against the associated table, no matter which user is connected

• A trigger can be either a database trigger or an application trigger.

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Designing Triggers 须注意• Perform related actions• Use triggers for global operations

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ApplicationApplication

SQL> INSERT INTO EMP 2 . . .;

EMP tableEMP tableEMPNO 7838 7698 7369 7788

ENAMEKINGBLAKESMITHSCOTT

JOBPRESIDENTMANAGERCLERKANALYST

SAL50002850 8003000

CHECK_SAL triggerCHECK_SAL trigger

Database Trigger: Example

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Creating Triggers 语句的组成CREATE [OR REPLACE ] TRIGGER trigger__name{BEFORE |AFTER | INSTEAD OF}eventON {table_or_view_name}[FOR EACH ROW [WHEN condition ]]trigger_body

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Creating Triggers 语句的组成• Trigger timing: BEFORE or AFTER• Triggering event: INSERT or UPDATE

or DELETE• Table name: On table 名• Trigger type: Row or statement

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Creating Triggers 语句的组成• When clause: Restricting condition.– 如果在 W H E N 子句中指定 trigger con

dition 的话，则首先对该条件求值。触发器主体只有在该条件为真值时才运行。– W H E N 子句只适用于行级触发器。如果使用该子句的话，触发器体将只对满足由

W H E N 子句说明的条件的行执行。• Trigger body: DECLARE

BEGIN END;

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语句的组成Trigger Timing: When should the trigger fire?• BEFORE: The code in the trigger body

will execute before the triggering DML event.• AFTER: The code in the trigger body will

execute after the triggering DML event.

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语句的组成Trigger Timing: When should the trigger fire?• INSTEAD OF: The code in the trigger

body will execute instead of the the triggering statement. 可以定义在 VIEW 上 .

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语句的组成Triggering Event: What DML operation will cause the trigger to execute?• INSERT• UPDATE • DELETE• Any combination of the above ：之间用 or 连接– INSERT OR UPDATE: 在执行 INSERT 或 UP

DATE 时都会触发此 TRIGGER.

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语句的组成Trigger Type:How many times should the trigger body execute when the triggering event takes place?• Statement: The trigger body executes once for

the triggering event. • This is the default.

• Row: The trigger body executes once for each row affected by the triggering event.• 用 FOR EACH ROW 子句指定。

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语句的组成Trigger Body:What action should the trigger perform?• The trigger body is defined with an anonymous

PL/SQL block.[DECLARE]BEGIN[EXCEPTION]END;

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SQL> UPDATE emp 2 SET sal = sal * 1.1 3 WHERE deptno = 30;

Example Example

Statement and Row Triggers

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EMPNOEMPNO

78397839

76987698

77887788

ENAMEENAME

KINGKING

BLAKEBLAKE

SMITHSMITH

DEPTNODEPTNO

3030

3030

3030

BEFORE statement triggerBEFORE statement trigger

BEFORE row triggerBEFORE row triggerAFTER row triggerAFTER row triggerBEFORE row triggerBEFORE row triggerAFTER row triggerAFTER row triggerBEFORE row triggerBEFORE row triggerAFTER row triggerAFTER row trigger

AFTER statement triggerAFTER statement trigger

Firing Sequence of Database Triggers on Multiple Rows

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触发器的触发顺序触发器是在 D M L 语句运行时激发的。下面是执行 D M L 语句的算法步骤：1 ) 如果有语句之前级触发器的话，先运行该触发器。2 ) 对于受语句影响每一行：• a. 如果有行之前级触发器的话，运行该触发器。• b. 执行该语句本身。• c. 如果有行之后级触发器的话，运行该触发器。

3 ) 如果有语句之后级触发器的话，运行该触发器。

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Before Statement Trigger: Example

EXAMPLE:trigger_test.txt

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Creating a Row Trigger

CREATE [OR REPLACE] TRIGGER trigger_nametiming event1 [OR event2 OR event3]ON table_name [REFERENCING OLD AS old | NEW AS new]FOR EACH ROW[WHEN condition]PL/SQL block;

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SQL>CREATE OR REPLACE TRIGGER audit_emp 2 AFTER DELETE OR INSERT OR UPDATE ON emp 3 FOR EACH ROW 4 BEGIN 5 IF DELETING THEN 6 UPDATE audit_table SET del = del + 1 7 WHERE user_name = user AND table_name = 'EMP' 8 AND column_name IS NULL; 9 ELSIF INSERTING THEN 10 UPDATE audit_table SET ins = ins + 1 11 WHERE user_name = user AND table_name = 'EMP' 12 AND column_name IS NULL; 13 ELSIF UPDATING ('SAL') THEN 14 UPDATE audit_table SET upd = upd + 1 15 WHERE user_name = user AND table_name = 'EMP' 16 AND column_name = 'SAL'; 17 ELSE /* The data manipulation operation is a general UPDATE. */ 18 UPDATE audit_table SET upd = upd + 1 19 WHERE user_name = user AND table_name = 'EMP' 20 AND column_name IS NULL; 21 END IF; 22 END; 23 /

After Row Trigger: Example

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行级触发器的相关标识1. 行级触发器是按触发语句所处理的行激发的。在触发器内部，我们可以访问正在处理中的行的数据。2. 这种访问是通过两个相关的标识符：• : o l d 和 : n e w 实现的。3. ： new.field 只有在该字段位于触发表中时才是合法的。

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行级触发器的相关标识触发语句I N S E RT (: o l d): 无定义 , 所有字段为空 N U L L (: n e w): 该语句结束时将插入的值U P D AT E (: o l d): 更新前行的原始值(: n e w): 该语句结束时将更新的值D E L E T E (: o l d): 行删除前的原始值(: n e w): 无定义 - 所有字段为空 N U L L

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行级触发器的相关标识引用子句1. 我们可以根据需要使用子句 R E F E R E N C I N

G 来为 :new 和 :old 指定一个不同的名称。2. 该子句可以在触发事件之后， W H E N 子句之前使用，3. 其语法如下：4. REFERENCING [OLD AS :old_name] [NEW AS

:new_name]5. 在触发器体内，我们可以使用 : old_name 和 : ne

w_name 来代替 : old 和 : new 。

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行级触发器的相关标识EXAMPLE:trigger_row.txt

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Differentiating Between Triggers and Stored Procedures

Triggers

Use CREATE TRIGGER

Data dictionary contains source and p-code

Implicitly invoked

COMMIT, SAVEPOINT, ROLLBACK not allowed

Procedure

Use CREATE PROCEDURE

Data dictionary contains source and p-code

Explicitly invoked

COMMIT, SAVEPOINT, ROLLBACK allowed

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ALTER TRIGGER trigger_name DISABLE | ENABLE

Managing TriggersDisable or Re-enable a database triggerDisable or Re-enable a database trigger

ALTER TABLE table_name DISABLE | ENABLE ALL TRIGGERS

Disable or Re-enable all triggers for a tableDisable or Re-enable all triggers for a table

ALTER TRIGGER trigger_name COMPILE

Recompile a trigger for a tableRecompile a trigger for a table

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Removing Triggers

To remove a trigger from the database, use the DROP TRIGGER syntax:

DROP TRIGGER trigger_name

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Triggers 管理的方法• Rule 1: • Do not change data in the primary key, f

oreign key, or unique key columns of a constraining table （约束表） .

• Rule 2:• Do not read data from a mutating table（变异表） .

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Triggers 管理的方法• 系统对触发器将要访问的表和列有一些限制。为了定义这些限制，有必要来理解什么是变异表（ mut

ating table ）和约束表 (constraining table).

• 变异表就是当前被 D M L 语句修改的表。对触发器来说，变异表就是触发器在其上进行定义的表• A table is not considered mutating for STATEM

ENT triggers.

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Triggers 管理的方法

• 约束表是一种需要实施引用完整性约束而读入的表 , 即在– FOREIGN KEY(field) REFERENC

ES 参照表 (field)– 如：– FOREIGN KEY(deptno) REFERE

NCES dept_new(deptno);

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Triggering eventTriggering event

Trigger actionTrigger action

SQL> UPDATE emp 2 SET deptno = 20 3 WHERE deptno = 30;

EMP tableEMP tableEMPNO769876547499

ENAMEBLAKEMARTINALLEN

DEPTNO303030

Referential integrityReferential integrity DEPT_new tableDEPT_new tableDNAMEACCOUNTINGRESEARCHSALESOPERATIONS

DEPTNO10203040

Failure ConstrainingConstrainingtabletable

AFTER UPDATEAFTER UPDATErowrow

xxxxxxxxxxxxxxxxxxxxxxxxxxxxvvvvvvvvvvvvvvvvvvvvvvvvvvvvxxxxxxxxxxxxxxxxxxxxxxxxxxxxvvvvvvvvvvvvvvvvvvvvvvvvvvvvxxxxxxxxxxxxxxxxxxxxxxxxxxxx

TriggeredTriggeredtabletable

CASCADE_UPDATESCASCADE_UPDATEStriggertrigger

Changing Data in a Constraining Table

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Constraining Table: Example

CREATE OR REPLACE TRIGGER cascade_updates AFTER UPDATE OF deptno on emp FOR EACH ROW BEGIN UPDATE dept_new SET dept_new.deptno = :new.deptno

WHERE dept_new.deptno = :old.deptno; END;

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Constraining Table: Example

EXAMPLE:constraint_trigger.txt

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Trigger eventTrigger event

SQL> UPDATE emp 2 SET sal = 1500 3 WHERE ename = 'SMITH';

EMP tableEMP tableEMPNO736976987788

ENAMESMITHBLAKESCOTT

SAL150028503000

Failure

Trigged table/Trigged table/mutating tablemutating table

BEFOREBEFOREUPDATEUPDATErowrow

CHECK_SALARYCHECK_SALARYtriggertrigger

Reading Data from a Mutating Table

JOBCLERKMANAGERANALYST

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Mutating Table: Example

EXAMPLE:1. 在 insert ,update 员工 salary 之前，检查新指定的

salary 。如果新指定的 salary 高于所有员工中的最高工资 , 或低于所有员工中的最低工资，则提示错误.

mutating_table.txt

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Trigger 的功能• Security Security – :trigger_test.txt:trigger_test.txt 中的中的 secure_empsecure_emp

• Auditing – :trigger_row txttxt 中的中的 audit_emp_v

alues• Data integrity• Referential integrity• Table replication• Event logging

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小结•Trigger•CREATE Trigger•MANAGE Trigger•使用 Trigger