--创建测试表
CREATE TABLE emp (empname text,salary integer,last_date timestamp,last_user text
);--创建触发器函数
CREATE FUNCTION emp_stamp() RETURNS trigger AS $emp_stamp$BEGIN-- 检查 empname 以及 salaryIF NEW.empname IS NULL THENRAISE EXCEPTION 'empname cannot be null';END IF;IF NEW.salary IS NULL THENRAISE EXCEPTION '% cannot have null salary', NEW.empname;END IF;-- 谁会倒贴钱为我们工作？IF NEW.salary < 0 THENRAISE EXCEPTION '% cannot have a negative salary', NEW.empname;END IF;-- 记住谁在什么时候改变了工资单NEW.last_date := current_timestamp;NEW.last_user := current_user;RETURN NEW;END;
$emp_stamp$ LANGUAGE plpgsql;--创建触发器
CREATE TRIGGER emp_stamp BEFORE INSERT OR UPDATE ON empFOR EACH ROW EXECUTE PROCEDURE emp_stamp();--测试触发器
test=# insert into emp values ('John');  --salary为空，触发器报错
ERROR:  John cannot have null salary
CONTEXT:  PL/pgSQL function emp_stamp() line 7 at RAISEtest=# insert into emp values (null,1200);   --empname为空，触发器报错
ERROR:  empname cannot be null
CONTEXT:  PL/pgSQL function emp_stamp() line 4 at RAISEtest=# insert into emp values ('John',-200); --salary为负数，触发器报错
ERROR:  John cannot have a negative salary
CONTEXT:  PL/pgSQL function emp_stamp() line 10 at RAISEtest=# insert into emp values ('Bob',1200);  --成功插入正常数据，并记录了最后操作时间和操作用户
INSERT 0 1
test=# select * from emp;empname | salary |         last_date          | last_user
---------+--------+----------------------------+-----------Bob     |   1200 | 2017-08-09 17:39:23.671957 | postgres
(1 row)

--创建测试表
create table emp (
empname text not null,
salary integer
);--创建审计表
create table emp_audit(
operation       char(1)   not null,
stamp           timestamp not null,
userid          text      not null,
empname         text      not null,
salary          integer
);--创建触发器函数
create or replace function process_emp_audit() returns trigger as $emp_audit$
beginif (TG_OP = 'DELETE') theninsert into emp_audit select 'D',now(),user,old.*;return old;elsif (TG_OP = 'UPDATE') theninsert into emp_audit select 'U',now(),user,new.*;return new;elsif (TG_OP = 'INSERT') theninsert into emp_audit select 'I',now(),user,new.*;return new;end if;return null;
end;
$emp_audit$ language plpgsql;--创建触发器
create trigger emp_audit
after insert or update or delete on emp
for each row execute procedure process_emp_audit();--测试触发器
test=# insert into emp values ('John',1200);
INSERT 0 1
test=# select * from emp_audit;operation |           stamp            |  userid  | empname | salary
-----------+----------------------------+----------+---------+--------I         | 2017-08-09 18:18:10.189772 | postgres | John    |   1200
(1 row)