多表操作

1.根据两个表达关系，搜索两个表。
select * from artist,painting where artist.a_id = painting.a_id;
2.另一种方法，用inner join代替逗号,where变成on。
select * from artist inner join painting on artist.a_id = painting.a_id;
3.如果两个表达字段a_id名字相同，可以用using达到相同的效果。
select * from artist inner join painting using(a_id);
这样查询出的结果只返回一个a_id。
4.通常是使用on或using来制定如何连接表，使用where限制选择已连接的行。例如：
select * from artist inner join painting on artist.a_id = painting.a_id where painting.state='北京';
5.再添加一张表，实现更复杂的多表查询。
select artist.name,painting.title,states.name,painting.price
from artist inner join painting inner join states
on artist.a_id=painting.a_id and painting.state=states.abbrev;
6.哪些是梵高的作品？可以这样查询。
select painting.title
from artist inner join painting on artist.a_id=painting.a_id
where artist.name='梵高';
7.蒙娜丽莎是谁画的?可以这样查。
select artist.name
from artist inner join painting on artist.a_id=painting.a_id
where painting.title = '蒙娜丽莎';
8.你在北京或台湾买了那些画？
select distinct artist.name
from artist inner join painting on artist.a_id=painting.a_id
where painting.state in('台湾','北京');
9.这里的distinct是不同的意思，就是说每个画家的名字你只想显示一次。
你甚至可以产生表达摘要，比如，你想知道，每个画家各有多少作品。
select artist.name,count(*) as '画的数量'
from artist inner join painting on artist.a_id=painting.a_id
group by artist.name;
10.你可以显示每个画家花费了多少钱，包括综合和每幅作品的平均花费。
select artist.name,
count(*) as '画的数量',
sum(painting.price) as 'total price',
avg(painting.price) as 'average price'
from artist inner join painting on artist.a_id=painting.a_id
group by artist.name;
11.
'select qg_singlepage.qg_id,qg_name,qg_filename,qg_display,qg_location,qg_show from ' .
'qg_singlepage inner join qg_termianl using(qg_uid) where ' .
'qg_termianl.qg_name like \'%'.$like.'%\' and qg_singlepage.qg_uid like \'%'.$_GET['id'].'%\' ' .
'limit '.$Page->firstRow.','.$Page->listRows limit 0,2;