create view pb_quarters as
select * from piggy_bank
where coin = 'Q'
select * from pb_quarters
create view pb_dimes as
select * from piggy_bank
where coin = 'D'
select * from pb_dimes
create view pb_neckel as
select * from piggy_bank
where coin = 'N' with check option
select * from pb_neckel
insert into pb_quarters values('Q', '1993')
select * from pb_quarters
insert into pb_quarters values('D', '1942')
select * from pb_quarters
1.当插入视图的值在视图中不存在，则插入无效，如果‘D’不存在，则插入无效，而Q存在，则insert 有效。
