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

话不多说，先上个对于各种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

 

4、笛卡尔积

select * from Table_a ,Table_b

原文链接：

https://blog.youkuaiyun.com/Megustas_JJC/article/details/86092980?ops_request_misc=%257B%2522request%255Fid%2522%253A%2522159039481719195162510845%2522%252C%2522scm%2522%253A%252220140713.130102334..%2522%257D&request_id=159039481719195162510845&biz_id=0&utm_medium=distribute.pc_search_result.none-task-blog-2~all~first_rank_v2~rank_v25-2-86092980.first_rank_v2_rank_v25&utm_term=out+join