SQL联接 外联接 内联接 完全联接 交叉联接

Posted 2020-07-01 whellote

联接分为:

内联接????????????????????????[inner join]

外联接????????(左外联接,右外联接)????????[left join/left outer join, right join/right outer join]

完全联接????????????????????[full join]

交叉联接????????????????????[cross join]

a表???? id????ebcid????name????????b表 ????uid????ebcid

????1????1????aa????????????1????1

????2????2????bb????????????1????2

????3????3????cc????????????1????3

????4????4????dd????????????2????2

????5????5????ee????????????2????3

内联接

select a.*, b.* from a inner join b on a.ebcid = b.ebcid

结果:

1????1????aa????1????1

2????2????bb????1????2

3????3????cc????1????3

2????2????bb????2????2

3????3????cc????2????3

?

左外联接

select a.*, b.* from a left join b on a.ebcid = b.ebcid

1????1????aa????1????1

2????2????bb????1????2

2????2????bb????2????2

3????3????cc????1????3

3????3????cc????2????3

4????4????dd

5????5????ee

?

右外联接(以右表为主,例子不够典型~~囧)

select a.*, b.* from a right join b on a.ebcid = b.ebcid

1????1????aa????1????1

2????2????bb????1????2

3????3????cc????1????3

2????2????bb????2????2

3????3????cc????2????3

?

完全联接

左右都是全的

交叉联接 (笛卡尔积)