学习目标

学习openGauss触发器

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）

课程学习

连接数据库

su - omm
gsql -r

1.创建源表及触发表

CREATE TABLE test_trigger_src_tbl(id1 INT, id2 INT, id3 INT) ;
CREATE TABLE test_trigger_des_tbl(id1 INT, id2 INT, id3 INT);

2.insert触发器

–创建触发器函数

CREATE OR REPLACE FUNCTION tri_insert_func() RETURNS TRIGGER AS
$$
DECLARE
BEGIN
INSERT INTO test_trigger_des_tbl VALUES(NEW.id1, NEW.id2, NEW.id3);
RETURN NEW;
END
$$ LANGUAGE PLPGSQL;

–创建INSERT触发器

CREATE TRIGGER insert_trigger
BEFORE INSERT ON test_trigger_src_tbl
FOR EACH ROW
EXECUTE PROCEDURE tri_insert_func();

–执行INSERT触发事件并检查触发结果

INSERT INTO test_trigger_src_tbl VALUES(100,200,300);

–查看触发操作生效

SELECT * FROM test_trigger_src_tbl;
SELECT * FROM test_trigger_des_tbl;

3.update触发器

–创建触发器函数

CREATE OR REPLACE FUNCTION tri_update_func() RETURNS TRIGGER AS
$$
DECLARE
BEGIN
UPDATE test_trigger_des_tbl SET id3 = NEW.id3 WHERE id1=OLD.id1;
RETURN OLD;
END
$$ LANGUAGE PLPGSQL;

–创建update触发器

CREATE TRIGGER update_trigger
AFTER UPDATE ON test_trigger_src_tbl
FOR EACH ROW
EXECUTE PROCEDURE tri_update_func();

–执行update触发事件并检查触发结果

UPDATE test_trigger_src_tbl SET id3=400 WHERE id1=100;

–查看触发操作生效

SELECT * FROM test_trigger_src_tbl;
SELECT * FROM test_trigger_des_tbl;

4.delete触发器

–创建触发器函数

CREATE OR REPLACE FUNCTION TRI_DELETE_FUNC() RETURNS TRIGGER AS
$$
DECLARE
BEGIN
DELETE FROM test_trigger_des_tbl WHERE id1=OLD.id1;
RETURN OLD;
END
$$ LANGUAGE PLPGSQL;

–创建delete触发器

CREATE TRIGGER delete_trigger
BEFORE DELETE ON test_trigger_src_tbl
FOR EACH ROW
EXECUTE PROCEDURE tri_delete_func();

–执行delete触发事件并检查触发结果

DELETE FROM test_trigger_src_tbl WHERE id1=100;

–查看触发操作生效

SELECT * FROM test_trigger_src_tbl;
SELECT * FROM test_trigger_des_tbl;  

5.修改触发器

–重命名

ALTER TRIGGER delete_trigger ON test_trigger_src_tbl RENAME TO delete_trigger_renamed;

–在系统表PG_TRIGGER中查看触发器

select * from PG_TRIGGER;

–查看表上的所有触发器

\dS+ test_trigger_src_tbl

6.禁用触发器

–禁用insert_trigger触发器

ALTER TABLE test_trigger_src_tbl DISABLE TRIGGER insert_trigger;

–执行INSERT

INSERT INTO test_trigger_src_tbl VALUES(100,200,300);

–查看触发操作没有生效

SELECT * FROM test_trigger_src_tbl;
SELECT * FROM test_trigger_des_tbl;

–禁用当前表上所有触发器

ALTER TABLE test_trigger_src_tbl DISABLE TRIGGER ALL;

7.删除触发器

DROP TRIGGER update_trigger ON test_trigger_src_tbl;
DROP TRIGGER delete_trigger_renamed ON test_trigger_src_tbl;      

课程作业

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 test_1 (a int,b int);
create table test_2 (a int,b int);

create function tri_insert returns trigger as
$$
declare
begin
insert into test_2 values(new.a,new.b);
return new;
end
$$ language plpgsql;

create trigger insert_trigger
before insert on test_1
for each row
execute procedure tri_insert();

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 test_1 values(1,2);
select * from test_1;
select * from test_2;

alter table test_1 disable trigger insert_trigger;
insert into test_1 values(2,3);
select * from test_1;
select * from test_2;

3.使用系统表PG_TRIGGER和\dS+查看触发器

select * from pg_trigger;
\ds+ test_1

4.重命名触发器

alter trigger insert_trigger on test_1 rename to insert_trigger_new;

5.删除触发器

drop trigger insert_trigger_new on test_1;

总结：为什么触发器还要专门写函数，直接在定义时将函数内容写进触发器不好吗