mysql連接查詢經典小例題，

mysql連接查詢經典小例題，

mysql連接查詢：

Mysql連接查詢支持多表連接

對同一張表可以重復連接多次(別名在多次連接同一張表時很重要)

例題1：

下面有2張表

teams表

比賽結果表：result

問題：

得出一張表:

主隊,客隊,比賽成績,比賽時間

方法一：(子查詢和連接查詢混合)

  step1:

select result.id, t_name as h_name,match_time,result from teams  join result on teams.t_id=result.h_id

step2:

select result.id ,t_name as g_name from teams  join result on teams.t_id=result.g_id

得到

step3:根據比賽的id 相等連接以上兩表即可

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

結果是出來了，有點繁瑣

方法二：多次連接查詢

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：

Teams表要連接2次所以要有別名

例題2：

現有下表 subject

求這樣一個表

父欄目名 ,子欄目名稱

連接查詢

自己連接自己更需要別名了

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

為方便練習，或得建表和數據填充sql請點擊獲取練習sql