1、觸發器類型
1）BEFORE 觸發器：在對表插入或更新之前執行該觸發器，允許使用CALL 和 SIGNAL SQL 語句；
2）BEFORE DELETE 觸發器：在刪除操作之前執行該觸發器；
3）AFTER 觸發器：在更新、插入或刪除操作之后執行。該觸發器用於更新反映表間關系和一致性的其他表中的數據，還用於確保數據完整性。AFTER 觸發器通常用於在特定情況下向用戶生成報警；
4）INSTEAD OF 觸發器：該觸發器支持對不支持插入、更新和刪除操作的視圖執行這些操作；
2、創建觸發器所需的權限
1）使用觸發器的模式ID必須擁有以下權限之一：
i)對定義 BEFORE 或 AFTER 觸發器的表擁有 ALTER 權限；
ii)對定義 INSTEAD OF 觸發器的視圖擁有 CONTROL 權限；
iiI)對定義 INSTEAD OF 觸發器的視圖擁有所有權；
iv)對定義觸發器的表或視圖的模式擁有 ALTERIN 權限；
v)SYSADM 或 DBADM 授權；
2）以及以下任意一種權限：
i)IMPLICIT_SCHEMA 數據庫授權（如果觸發器的隱式或顯式模式名稱不存在）；
ii)對模式的 CREATEIN 權限（如果觸發器的模式名稱引用現有的模式）；
3）假定授權 ID 沒有 SYSADM 和 DBADM 權限並且觸發器存在，此 ID 必須擁有以下所有權限：
i)對定義觸發器的表擁有 SELECT 權限 — 用於轉換變量和/或表；
ii)對在觸發的操作條件中引用的任意表或視圖的 SELECT 權限；
iii)調用觸發的指定 SQL 語句所需的權限；
3、創建觸發器語句
1）語法
.-NO CASCADE-.
>>-CREATE TRIGGER--trigger-name--+-+------------+--BEFORE-+----->
+-AFTER------------------+
'-INSTEAD OF-------------'
>--+-INSERT--------------------------+--ON--+-table-name-+------>
+-DELETE--------------------------+ '-view-name--'
'-UPDATE--+---------------------+-'
| .-,-----------. |
| V | |
'-OF----column-name-+-'
>--+------------------------------------------------------------------+-->
| .-------------------------------------------------. |
| V (1) (2) .-AS-. | |
'-REFERENCING------------------+-OLD--+----+--correlation-name-+-+-'
| .-AS-. |
+-NEW--+----+--correlation-name-+
| .-AS-. |
+-OLD TABLE--+----+--identifier-+
| .-AS-. |
'-NEW TABLE--+----+--identifier-'
>--+-FOR EACH ROW--------------+--| triggered-action |--------->
| (3) |
'--------FOR EACH STATEMENT-'
triggered-action
|--+-------------------------------------+---------------------->
| (4) |
'--------WHEN--(--search-condition--)-'
2）觸發器有三個主要組件：
i)觸發器事件；
ii)觸發器條件；
iii)觸發器操作；
3）示例：
i)簡單的 AFTER INSERT 觸發器
CREATE TRIGGER new_emp
AFTER INSERT ON employee
REFERENCING NEW AS n
FOR EACH ROW
INSERT INTO audit_emp VALUES (n.empno, 'Insert',0.0, current user, current timestamp)
ii)簡單的 AFTER DELETE 觸發器
CREATE TRIGGER purge_emp
AFTER DELETE ON employee
REFERENCING OLD AS o
FOR EACH ROW
INSERT INTO audit_emp VALUES (o.empno, 'Delete',0.0, current user, current timestamp)
iii)簡單的 AFTER UPDATE 觸發器
CREATE TRIGGER update_emp
AFTER UPDATE OF salary ON employee
REFERENCING OLD AS o NEW AS n
FOR EACH ROW
WHEN (n.salary <> o.salry)
INSERT INTO audit_emp VALUES (o.empno,'Update',n.salary,current user, current timestamp)
iv)簡單的 BEFORE UPDATE 觸發器
CREATE TRIGGER update_bemp
BEFORE UPDATE ON employee
REFERENCING OLD AS o NEW AS n
FOR EACH ROW
WHEN (n.salary = 60000.00)
SET n.salary = 75000.00)
4、觸發器的高級用法
1）INSTEAD OF 觸發器
--示例
CREATE TABLE "DB2INST1"."EMPLOYEES"
(
"EMPNO" CHAR(6) NOT NULL ,
"FIRSTNME" VARCHAR(12) NOT NULL ,
"LASTNAME" VARCHAR(15) NOT NULL ,
"PHONENO" CHAR(4) ,
"SALARY" DECIMAL(9,2)
)
CREATE VIEW employeev AS
SELECT empno, firstnme, lastname, phoneno
FROM employees
CREATE TRIGGER new_emp1
INSTEAD OF INSERT ON employeev
REFERENCING NEW AS n
FOR EACH ROW
INSERT INTO employees VALUES (n.empno, n.firstnme, n.lastname, n.phoneno, 0)
2）用觸發器處理 XML 數據
--示例
CREATE TRIGGER new_order
BEFORE INSERT ON purchaseorder
REFERENCING NEW AS N
FOR EACH ROW
SET (n.porder) = xmlvalidate(n.porder
ACCORDING TOXMLSCHEMA URI 'http://posample.org/order.xsd')
3）使用 SQL PL 語句擴展觸發器主體
i)語法
General Syntax Diagram for CREATE TRIGGER cont. SQL-procedure-statement |--+-CALL----------------------------------------------+--------| +-Compound SQL (Dynamic)----------------------------+ +-FOR-----------------------------------------------+ +-+-----------------------------------+--fullselect-+ | | .-,-----------------------. | | | | V | | | | '-WITH----common-table-expression-+-' | +-GET DIAGNOSTICS-----------------------------------+ +-IF------------------------------------------------+ +-INSERT--------------------------------------------+ +-ITERATE-------------------------------------------+ +-LEAVE---------------------------------------------+ +-MERGE---------------------------------------------+ +-searched-delete-----------------------------------+ +-searched-update-----------------------------------+ +-SET Variable--------------------------------------+ +-SIGNAL--------------------------------------------+ '-WHILE---------------------------------------------'
ii)從觸發器中調用存儲過程
CREATE PROCEDURE write_audit( IN p_empno CHAR(6),
IN p_txt CHAR(6),
IN p_salary DECIMAL(9,2),
IN p_user CHAR(8),
IN p_curtime TIMESTAMP )
BEGIN
INSERT INTO audit_emp VALUES ( p_empno, p_txt, p_salary, p_user, p_curtime )
END
CREATE TRIGGER new_emp
AFTER INSERT ON employee
REFERENCING NEW AS n
FOR EACH ROW
CALL write_audit( n.empno, 'Insert', 0.0, current user, current timestamp)
iii)使用 SQL PL 的 BEFORE INSERT 觸發器
CREATE TRIGGER business_rules
BEFORE INSERT ON empprojact
REFERENCING NEW AS n
FOR EACH ROW
BEGIN ATOMIC
-- Business Rule One (Project ending date Can't be NULL)
IF (n.emendate IS NULL) THEN
SET n.emendate = CURRENT date;
END IF;
-- Business Rule Two (Project ending date Can't end in last month of the year)
IF (n.emendate BETWEEN '2009-12-01' AND '2009-12-31') THEN
SIGNAL SQLSTATE '90000'
SET MESSAGE_TEXT = 'Business Rule violation - 90000';
END IF;
END