create view CityNum(城市號,城市名)
as
select * from
(
select 城市號,城市名 from MainCity
union
select 城市號,城市名 from 一般城市)derivedtbl

create view MainCity(城市號,城市名)
as
select 省會號+300,省會名 from 省會

create view NNRoutInfo(城城路段號,路段起點,路段終點)
as
select 路段號,b1.城市名,b2.城市名
from 鐵路網(wǎng) a,一般城市 b1,一般城市 b2
where b1.城市號=a.路段起點 and b2.城市號=a.路段終點

create view NMRoutInfo(城省路段號,路段起點,路段終點)
as
select 路段號,城市名,省會名
from 鐵路網(wǎng) a,一般城市 b,省會 c
where b.城市號=a.路段起點 and c.省會號+300=a.路段終點

create view MNRoutInfo(城省路段號,路段起點,路段終點)
as
select 路段號,省會名,城市名
from 鐵路網(wǎng) a,一般城市 b,省會 c
where  b.城市號=a.路段終點 and c.省會號+300=a.路段起點

create view MMRoutInfo(省省路段號,路段起點,路段終點)
as
select 路段號,b.省會名,c.省會名
from 鐵路網(wǎng) a,省會 b,省會 c
where b.省會號+300=a.路段起點 and c.省會號+300=a.路段終點

create view XMRoutInfo(路段號,路段起點,路段終點)
as
select *
from(
select *
from MMRoutInfo
union
select *
from NMRoutInfo)derivedtbl

create view NXRoutInfo(路段號,路段起點,路段終點)
as
select *
from(
select *
from NMRoutInfo
union
select *
from NNRoutInfo)derivedtbl

create view XNRoutInfo(路段號,路段起點,路段終點)
as
select *
from(
select *
from MNRoutInfo
union
select *
from NNRoutInfo)derivedtbl

create view MXRoutInfo(路段號,路段起點,路段終點)
as
select *
from(
select *
from MNRoutInfo
union
select *
from MMRoutInfo)derivedtbl