触发器的作用：触发器是对应用动作的响应机制，当应用对一个对象发起DML操作时，就会产生一个触发事件（Event），如果该对象上拥有该事件对应的触发器，那么就会检查触发器的触发条件（Condition）是否满足，如果满足触发条件，那么就会执行触发动作（Action）
1.创建源表和触发表，在源表上创建insert触发器，创建操作触发表的触发器函数
CREATE TABLE t_trigger_src_tbl(a INT, b INT, c INT);
CREATE TABLE t_trigger_des_tbl(a INT, b INT, c INT);
CREATE OR REPLACE FUNCTION tri_insert_func() RETURNS TRIGGER AS
$$
DECLARE
BEGIN
INSERT INTO t_trigger_des_tbl VALUES(NEW.a, NEW.b, NEW.c);
RETURN NEW;
END
$$ LANGUAGE PLPGSQL;
CREATE TRIGGER insert_trigger
BEFORE INSERT ON t_trigger_src_tbl
FOR EACH ROW
EXECUTE PROCEDURE tri_insert_func();
INSERT INTO t_trigger_src_tbl VALUES(100,200,300);
SELECT * FROM t_trigger_src_tbl;
SELECT * FROM t_trigger_des_tbl;
2.在源表上执行insert操作，查看触发操作是否生效；禁用触发器后，再次查看触发操作是否生效
INSERT INTO t_trigger_src_tbl VALUES(500,600,700);
SELECT * FROM t_trigger_src_tbl;
SELECT * FROM t_trigger_des_tbl;
ALTER TABLE t_trigger_src_tbl DISABLE TRIGGER insert_trigger;
INSERT INTO t_trigger_src_tbl VALUES(800,900,1000);
SELECT * FROM t_trigger_src_tbl;
SELECT * FROM t_trigger_des_tbl;
3.使用系统表PG_TRIGGER和\dS+查看触发器
select * from PG_TRIGGER;
\dS+ t_trigger_src_tbl
4.重命名触发器
ALTER TRIGGER insert_trigger ON t_trigger_src_tbl RENAME TO insert_trigger_n;
5.删除触发器
DROP TRIGGER insert_trigger_n ON t_trigger_src_tbl;
