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

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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