mysql的几种连接方式
2022/1/20 2:21:11
本文主要是介绍mysql的几种连接方式,对大家解决编程问题具有一定的参考价值,需要的程序猿们随着小编来一起学习吧!
测试数据
## 连接表测试数据 select * from aa; +----+--------+ | id | userid | +----+--------+ | 1 | 10 | | 2 | 11 | | 3 | 12 | | 4 | 13 | | 7 | 16 | | 8 | 17 | | 9 | 18 | +----+--------+ 7 rows in set (0.00 sec) select * from bb; +----+--------+ | id | userid | +----+--------+ | 1 | 16 | | 2 | 17 | | 3 | 18 | | 4 | 20 | +----+--------+ 4 rows in set (0.00 sec)
1.笛卡尔积
- 结果行数:左表行数*右表行数
+----+--------+----+--------+ | id | userid | id | userid | +----+--------+----+--------+ | 1 | 10 | 4 | 20 | | 1 | 10 | 3 | 18 | | 1 | 10 | 2 | 17 | | 1 | 10 | 1 | 16 | | 2 | 11 | 4 | 20 | | 2 | 11 | 3 | 18 | | 2 | 11 | 2 | 17 | | 2 | 11 | 1 | 16 | | 3 | 12 | 4 | 20 | | 3 | 12 | 3 | 18 | | 3 | 12 | 2 | 17 | | 3 | 12 | 1 | 16 | | 4 | 13 | 4 | 20 | | 4 | 13 | 3 | 18 | | 4 | 13 | 2 | 17 | | 4 | 13 | 1 | 16 | | 7 | 16 | 4 | 20 | | 7 | 16 | 3 | 18 | | 7 | 16 | 2 | 17 | | 7 | 16 | 1 | 16 | | 8 | 17 | 4 | 20 | | 8 | 17 | 3 | 18 | | 8 | 17 | 2 | 17 | | 8 | 17 | 1 | 16 | | 9 | 18 | 4 | 20 | | 9 | 18 | 3 | 18 | | 9 | 18 | 2 | 17 | | 9 | 18 | 1 | 16 | +----+--------+----+--------+ 28 rows in set (0.00 sec)
2.左连接(left join)
- 结果集是左表全部保留,右表关联不上用null表示
- 结果行数:左表行数
select * from aa left join bb on aa.userid=bb.userid; +----+--------+------+--------+ | id | userid | id | userid | +----+--------+------+--------+ | 7 | 16 | 1 | 16 | | 8 | 17 | 2 | 17 | | 9 | 18 | 3 | 18 | | 1 | 10 | NULL | NULL | | 2 | 11 | NULL | NULL | | 3 | 12 | NULL | NULL | | 4 | 13 | NULL | NULL | +----+--------+------+--------+ 7 rows in set (0.00 sec)
3.右连接(right join)
- 结果集是右表全部保留,左表关联不上用null表示
- 结果行数:右表行数
select * from aa right join bb on aa.userid=bb.userid; +------+--------+----+--------+ | id | userid | id | userid | +------+--------+----+--------+ | 7 | 16 | 1 | 16 | | 8 | 17 | 2 | 17 | | 9 | 18 | 3 | 18 | | NULL | NULL | 4 | 20 | +------+--------+----+--------+ 4 rows in set (0.00 sec)
4.内连接(inner join)
- 等值连接,结果集保留量表中的交接的记录
select * from aa inner join bb on aa.userid=bb.userid; +----+--------+----+--------+ | id | userid | id | userid | +----+--------+----+--------+ | 7 | 16 | 1 | 16 | | 8 | 17 | 2 | 17 | | 9 | 18 | 3 | 18 | +----+--------+----+--------+ 3 rows in set (0.00 sec)
5.左表独有
- 查询左表独有的数据
select * from aa left join bb on aa.userid=bb.userid where bb.userid is null; +----+--------+------+--------+ | id | userid | id | userid | +----+--------+------+--------+ | 1 | 10 | NULL | NULL | | 2 | 11 | NULL | NULL | | 3 | 12 | NULL | NULL | | 4 | 13 | NULL | NULL | +----+--------+------+--------+ 4 rows in set (0.00 sec)
6.右表独有
- 查询右表独有的数据
select * from aa right join bb on aa.userid=bb.userid where aa.userid is null; +------+--------+----+--------+ | id | userid | id | userid | +------+--------+----+--------+ | NULL | NULL | 4 | 20 | +------+--------+----+--------+ 1 row in set (0.00 sec)
7.全连接
- 关联表的所有记录
- 通过的union实现
- 结果行数:左表行数+右表行数
select * from aa left join bb on aa.userid=bb.userid union select * from aa right join bb on aa.userid=bb.userid; +------+--------+------+--------+ | id | userid | id | userid | +------+--------+------+--------+ | 7 | 16 | 1 | 16 | | 8 | 17 | 2 | 17 | | 9 | 18 | 3 | 18 | | 1 | 10 | NULL | NULL | | 2 | 11 | NULL | NULL | | 3 | 12 | NULL | NULL | | 4 | 13 | NULL | NULL | | NULL | NULL | 4 | 20 | +------+--------+------+--------+ 8 rows in set (0.00 sec)
8.并集去交集
select * from aa left join bb on aa.userid=bb.userid where bb.userid is null union select * from aa right join bb on aa.userid=bb.userid where aa.userid is null; +------+--------+------+--------+ | id | userid | id | userid | +------+--------+------+--------+ | 1 | 10 | NULL | NULL | | 2 | 11 | NULL | NULL | | 3 | 12 | NULL | NULL | | 4 | 13 | NULL | NULL | | NULL | NULL | 4 | 20 | +------+--------+------+--------+ 5 rows in set (0.00 sec)
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