MySQL中的七种常见通用的join查询

Posted 2021-07-05 活跃的咸鱼

常见通用的join查询

我用下面两张表来演示上面七种情况：

t_nation表

t_hero表

1.A∩B (内连接 B图)

select * from t_hero as h join
 t_nation n on h.hc_id=n.n_id;

2.A－B ( D图)

select * from t_hero as h left join 
t_nation as n on h.hc_id=n.n_id where n.n_id is null;

3.B－A (E图)

select * from t_hero as h right join 
t_nation as n on h.hc_id=n.n_id where h.h_id is null;

4.A∪B (F图 全外连接 mysql不支持)

select * from t_hero as h right join 
t_nation as n on h.hc_id=n.n_id
union
select * from t_hero as h left join 
t_nation as n on h.hc_id=n.n_id;

5.A－B∪ A∩B （A图 左连接）

select * from t_hero as h left join
 t_nation as n  on h.hc_id=n.n_id 

6.B－A∪ A∩B （B图 右连接）

select * from t_hero as h right join
 t_nation as n  on h.hc_id=n.n_id 

7.A－B∪B－A (G图)

select * from t_hero as h right join
 t_nation as n  on h.hc_id=n.n_id where h.hc_id is null
union
select * from t_hero as h left join 
t_nation as n  on h.hc_id=n.n_id where n.n_id is null;