Mysql中inner join、left join、right join的分析

Mysql中inner join、left join、right join的分析

    先来看一张图（引自百度百科）

下面我们举例分析哈，看表格:

table_A

id	a	b
1	a1	b1
2	a2	b2

table_B

id	a	c
1	a1	c1
3	a2	c2

1. inner join ：取主从表的交集

select * from table_A as t1 inner join table_B as t2 on t1.id = t2.id;

inner join 结果

table_A.id	table_A.a	b	table_B.id	table_B.a	c
1	a1	b1	1	a1	c1

2. left join : 取主表加交集

select * from table_A as t1 left join table_B as t2 on t1.id = t2.id;

left join 结果

table_A.id	table_A.a	b	table_B.id	table_B.a	c
1	a1	b1	1	a1	c1
2	a2	b2	null	null	null

3. right join : 取从表加交集

select * from table_A as t1 right join table_B as t2 on t1.id = t2.id;

left join 结果

table_A.id	table_A.a	b	table_B.id	table_B.a	c
1	a1	b1	1	a1	c1
null	null	null	3	a2	c2