【数据库】触发器

1.格式

create trigger trigger_name
　　on {table_name | view_name}
　　{for | After | Instead of }
　　[ insert, update,delete ]
　　as
　　sql_statement

2.例子(若分数增加了10%，则记录到另一个表中）

create trigger sc_t
after update of grade on sc
referencing 
   oldrow as oldtuple
   newrow as newtuple
for each row
when (newtuple.grade >= 1.1 *oldtuple.grade)
insert into sc_u (sno,cno,oldgrade,newgrade)
values(oldtuple.sno,oldtuple.cno,oldtuple.grade,newtuple.grade)

3.例子（将增加的学生个数记录到表中）

create trigger sc_t
after inserted
referencing 
   new table as delta
for each statement
insert into studentInsertlog(Numbers)
select count(*) from delta

 4.例子（工资不得低于4000，否则则修改为4000）

create trigger insert_or_update_sal
before insert or update on teacher
referencing new row as newtuple
for each row
begin 
if (newtuple.kob='教授')and(newtuple.sal<4000)
  then newtuple.sal=4000
end if 
end