MySQL连接查询相信大家都有所了解,连接查询是在数据库查询操作的时候经常用到的,下面就为您介绍MySQL连接查询
[b]mysql连接查询:[/b]支持多表连接
对同一张表可以重复连接多次(别名在多次连接同一张表时很重要)
[b]例题1:[/b]
下面有2张表
teams表
[img]http://files.jb51.net/file_images/article/201507/201507241525323.png[/img]
比赛结果表:result
[img]http://files.jb51.net/file_images/article/201507/201507241525324.png[/img]
问题:
得出一张表:主队,客队,比赛成绩,比赛时间
[b]方法一:子查询和连接查询混合[/b]
[b] step1:[/b]
select result.id, t_name as h_name,match_time,result from teams join result on teams.t_id=result.h_id
[img]http://files.jb51.net/file_images/article/201507/201507241525325.png[/img]
[b]step2:[/b]
select result.id ,t_name as g_name from teams join result on teams.t_id=result.g_id
得到
[img]http://files.jb51.net/file_images/article/201507/201507241525336.png[/img]
[b]step3[/b]:根据比赛的id 相等连接以上两表即可
select t1.id,h_name,g_name,result,match_time from
(select result.id, t_name as h_name,match_time,result from teams join result on teams.t_id=result.h_id) as t1
join
(select result.id ,t_name as g_name from teams join result on teams.t_id=result.g_id) as t2
on t1.id=t2.id;
即可得到
[img]http://files.jb51.net/file_images/article/201507/201507241525337.png[/img]
结果是出来了,有点繁琐
[b]方法二:多次连接查询[/b]
select result.id,t1.t_name as h_name ,t2.t_name as g_name ,result,match_time from result
join
teams as t1 on result.h_id=t1.t_id
join
teams as t2 on t2.t_id=result.g_id;
即可得到:
[img]http://files.jb51.net/file_images/article/201507/201507241525338.png[/img]
Teams表要连接2次所以要有别名
[b]例题2:[/b]
现有下表 subject
[img]http://files.jb51.net/file_images/article/201507/201507241525339.png[/img]
求这样一个表
父栏目名 ,子栏目名称
连接查询
自己连接自己更需要别名了
select t1.name as p_name,t2.name as son_name from subject as t1 join subject as t2 on t1.id=t2.pid;
即可得到
[img]http://files.jb51.net/file_images/article/201507/2015072415253310.png[/img]
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