数据库查询问题

Question

1.数据表有三个

     A:   a   b 
     B:   b   c
     C:   c   d

2.想查询A的a和C的d字段。
3.请输入代码

select A.a,C.d
from A
inner join B on A.b=B.b
inner join C on C.c=B.c
where A.b=B.b and C.c=B.c;

4.不会SQL，求指教下

Answer 1

select A.a,C.d
from A
inner join B on A.b=B.b
inner join C on C.c=B.c;

on就是配置关联关系，不需要再在where条件里面加上了

Answer 2

可以用内连跟做链接来关联查询
比如.
select A.a,C.d from a as A
left join B as B on A.b=B.b
left join C as C on C.c=B.c

Answer 3

SELECT tablesong.songname, 
       tablesinger.singername 
FROM   tablesong 
       INNER JOIN tablesongsinger1 
               ON tablesong.songindex = tablesongsinger1.songindex 
       INNER JOIN tablesinger 
               ON tablesinger.singerindex = tablesongsinger1.singerindex