create 表2 (a21 char(5)primary key, a22 varchar(25))
create 表1
( a1 char(10)primary key,
a2 char(5)REFERENCES 表1 (a21) ON DELETE CASCADE ON UPDATE CASCADE,
a3 varchar(10)
)
create 表1
( a1 char(10)primary key,
a2 char(5)REFERENCES 表1 (a21) ON DELETE CASCADE ON UPDATE CASCADE,
a3 varchar(10)
)
是级联更新
当你更新,删除表1的a21 ,表2中的记录也会更改看看help吧