SQL中join的用法解析（inner join、full out join、left join）

版权声明：本文为CSDN博主「Megustas_JJC」的原创文章，遵循 CC 4.0 BY-SA 版权协议，转载请附上原文出处链接及本声明。

原文链接：https://blog.csdn.net/Megustas_JJC/article/details/86092980

对于各种join情况的总结图：

例如有如下关系的数据：

1、inner join

 

select * from Table_a
join Table_b on Table_a.id_a = Table_b.id_b

 

2.1、full outer join等于full join

 

select * from Table_a
full join Table_b
on Table_a.id_a = Table_b.id_b

2.2、full outer join but a.Key is null or b.Key is null

 

select * from Table_a
full outer join Table_b
on Table_a.id_a = Table_b.id_b
where Table_a.id_a is null or Table_b.id_b is null

3.1、left outer join等于left join

 

select * from Table_a
left join Table_b on Table_a.id_a = Table_b.id_b

 

3.2、left outer join but b.Key is null

 

select * from Table_a

left outer join Table_b on Table_a.id_a = Table_b.id_b

where Table_b.id_b is null

 

笛卡尔积
select * from Table_a ,Table_b

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版权声明：本文为CSDN博主「Megustas_JJC」的原创文章，遵循 CC 4.0 BY-SA 版权协议，转载请附上原文出处链接及本声明。
原文链接：https://blog.csdn.net/Megustas_JJC/article/details/86092980