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MySQL中join用法解析

黄舟
Lepaskan: 2017-02-27 11:54:42
asal
1832 orang telah melayarinya


MySQL中join用法解析


实例数据库如下:
student表:

mysql> select * from student;
+-----------+-----------+------+------+-------+
| Sno       | Sname     | Ssex | Sage | Sdept |
+-----------+-----------+------+------+-------+
| 201215121 | 李勇      | 男   |   22 | CS    |
| 201215122 | 刘晨      | 女   |   19 | CS    |
| 201215123 | 王敏      | 女   |   18 | MA    |
| 201215125 | 张立      | 男   |   19 | IS    |
| 201215128 | 陈冬      | 男   |   18 | IS    |
| 201215126 | 张成民    | 男   |   18 | CS    |
+-----------+-----------+------+------+-------+6 rows in set (0.00 sec)
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sc表:

mysql> select * from sc;
+-----------+------+-------+
| Sno       | Cno  | Grade |
+-----------+------+-------+
| 201215121 |    1 |    92 |
| 201215121 |    2 |    85 |
| 201215121 |    3 |    88 |
| 201215122 |    2 |    90 |
| 201215122 |    3 |    80 |
| 201215128 |    1 |    78 |
+-----------+------+-------+6 rows in set (0.00 sec)
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LEFT JOIN(左连接)

这里写图片描述
sql语句如下:

select * from student left join sc on student.Sno=sc.Sno;
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运行结果如下:

+-----------+-----------+------+------+-------+-----------+------+-------+
| Sno       | Sname     | Ssex | Sage | Sdept | Sno       | Cno  | Grade |
+-----------+-----------+------+------+-------+-----------+------+-------+
| 201215121 | 李勇      | 男   |   22 | CS    | 201215121 |    1 |    92 |
| 201215121 | 李勇      | 男   |   22 | CS    | 201215121 |    2 |    85 |
| 201215121 | 李勇      | 男   |   22 | CS    | 201215121 |    3 |    88 |
| 201215122 | 刘晨      | 女   |   19 | CS    | 201215122 |    2 |    90 |
| 201215122 | 刘晨      | 女   |   19 | CS    | 201215122 |    3 |    80 |
| 201215128 | 陈冬      | 男   |   18 | IS    | 201215128 |    1 |    78 |
| 201215123 | 王敏      | 女   |   18 | MA    |      NULL | NULL |  NULL |
| 201215125 | 张立      | 男   |   19 | IS    |      NULL | NULL |  NULL |
| 201215126 | 张成民    | 男   |   18 | CS    |      NULL | NULL |  NULL |
+-----------+-----------+------+------+-------+-----------+------+-------+
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在此例中left join 是以student表中的记录为基础,student表可以看成左表,sc表可以看成右表,左表中的记录会完全显示出来,加上匹配到的右表,如果左边没有匹配到,则其余部分显示为null。

USING字句

using字句和on字句,类似,但结果略有不同。
例如:

mysql> select student.Sno,Sname,Grade from student left join sc on student.Sno=sc.Sno;
+-----------+-----------+-------+
| Sno       | Sname     | Grade |
+-----------+-----------+-------+
| 201215121 | 李勇      |    92 |
| 201215121 | 李勇      |    85 |
| 201215121 | 李勇      |    88 |
| 201215122 | 刘晨      |    90 |
| 201215122 | 刘晨      |    80 |
| 201215128 | 陈冬      |    78 |
| 201215123 | 王敏      |  NULL |
| 201215125 | 张立      |  NULL |
| 201215126 | 张成民    |  NULL |
+-----------+-----------+-------+
9 rows in set (0.00 sec)
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以上等价于

select Sno,Sname,Grade from student left join sc using(Sno);
+-----------+-----------+-------+
| Sno       | Sname     | Grade |
+-----------+-----------+-------+
| 201215121 | 李勇      |    92 |
| 201215121 | 李勇      |    85 |
| 201215121 | 李勇      |    88 |
| 201215122 | 刘晨      |    90 |
| 201215122 | 刘晨      |    80 |
| 201215128 | 陈冬      |    78 |
| 201215123 | 王敏      |  NULL |
| 201215125 | 张立      |  NULL |
| 201215126 | 张成民    |  NULL |
+-----------+-----------+-------+
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不同的地方,例如:

select * from student left join sc on student.Sno=sc.Sno;
+-----------+-----------+------+------+-------+-----------+------+-------+
| Sno       | Sname     | Ssex | Sage | Sdept | Sno       | Cno  | Grade |
+-----------+-----------+------+------+-------+-----------+------+-------+
| 201215121 | 李勇      | 男   |   22 | CS    | 201215121 |    1 |    92 |
| 201215121 | 李勇      | 男   |   22 | CS    | 201215121 |    2 |    85 |
| 201215121 | 李勇      | 男   |   22 | CS    | 201215121 |    3 |    88 |
| 201215122 | 刘晨      | 女   |   19 | CS    | 201215122 |    2 |    90 |
| 201215122 | 刘晨      | 女   |   19 | CS    | 201215122 |    3 |    80 |
| 201215128 | 陈冬      | 男   |   18 | IS    | 201215128 |    1 |    78 |
| 201215123 | 王敏      | 女   |   18 | MA    |      NULL | NULL |  NULL |
| 201215125 | 张立      | 男   |   19 | IS    |      NULL | NULL |  NULL |
| 201215126 | 张成民    | 男   |   18 | CS    |      NULL | NULL |  NULL |
+-----------+-----------+------+------+-------+-----------+------+-------+
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select * from student left join sc using (sno);
+-----------+-----------+------+------+-------+------+-------+
| Sno       | Sname     | Ssex | Sage | Sdept | Cno  | Grade |
+-----------+-----------+------+------+-------+------+-------+
| 201215121 | 李勇      | 男   |   22 | CS    |    1 |    92 |
| 201215121 | 李勇      | 男   |   22 | CS    |    2 |    85 |
| 201215121 | 李勇      | 男   |   22 | CS    |    3 |    88 |
| 201215122 | 刘晨      | 女   |   19 | CS    |    2 |    90 |
| 201215122 | 刘晨      | 女   |   19 | CS    |    3 |    80 |
| 201215128 | 陈冬      | 男   |   18 | IS    |    1 |    78 |
| 201215123 | 王敏      | 女   |   18 | MA    | NULL |  NULL |
| 201215125 | 张立      | 男   |   19 | IS    | NULL |  NULL |
| 201215126 | 张成民    | 男   |   18 | CS    | NULL |  NULL |
+-----------+-----------+------+------+-------+------+-------+
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重复的Sno列,如果用on字句会被输出两次

RIGHT JOIN(右连接)

同LEFT JOIN,只不过以右表为基础,例如:

 select * from student right join sc using (sno);
+-----------+------+-------+--------+------+------+-------+
| Sno       | Cno  | Grade | Sname  | Ssex | Sage | Sdept |
+-----------+------+-------+--------+------+------+-------+
| 201215121 |    1 |    92 | 李勇   | 男   |   22 | CS    |
| 201215121 |    2 |    85 | 李勇   | 男   |   22 | CS    |
| 201215121 |    3 |    88 | 李勇   | 男   |   22 | CS    |
| 201215122 |    2 |    90 | 刘晨   | 女   |   19 | CS    |
| 201215122 |    3 |    80 | 刘晨   | 女   |   19 | CS    |
| 201215128 |    1 |    78 | 陈冬   | 男   |   18 | IS    |
+-----------+------+-------+--------+------+------+-------+
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INNER JOIN(相等连接或内连接)

这里写图片描述

不会显示以谁为基础,只会显示符合条件的记录

 select * from student inner join sc on student.Sno=sc.Sno;
+-----------+--------+------+------+-------+-----------+------+-------+
| Sno       | Sname  | Ssex | Sage | Sdept | Sno       | Cno  | Grade |
+-----------+--------+------+------+-------+-----------+------+-------+
| 201215121 | 李勇   | 男   |   22 | CS    | 201215121 |    1 |    92 |
| 201215121 | 李勇   | 男   |   22 | CS    | 201215121 |    2 |    85 |
| 201215121 | 李勇   | 男   |   22 | CS    | 201215121 |    3 |    88 |
| 201215122 | 刘晨   | 女   |   19 | CS    | 201215122 |    2 |    90 |
| 201215122 | 刘晨   | 女   |   19 | CS    | 201215122 |    3 |    80 |
| 201215128 | 陈冬   | 男   |   18 | IS    | 201215128 |    1 |    78 |
+-----------+--------+------+------+-------+-----------+------+-------+
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以上语句等同于:

select * from student,sc where student.Sno=sc.Sno;
+-----------+--------+------+------+-------+-----------+------+-------+
| Sno       | Sname  | Ssex | Sage | Sdept | Sno       | Cno  | Grade |
+-----------+--------+------+------+-------+-----------+------+-------+
| 201215121 | 李勇   | 男   |   22 | CS    | 201215121 |    1 |    92 |
| 201215121 | 李勇   | 男   |   22 | CS    | 201215121 |    2 |    85 |
| 201215121 | 李勇   | 男   |   22 | CS    | 201215121 |    3 |    88 |
| 201215122 | 刘晨   | 女   |   19 | CS    | 201215122 |    2 |    90 |
| 201215122 | 刘晨   | 女   |   19 | CS    | 201215122 |    3 |    80 |
| 201215128 | 陈冬   | 男   |   18 | IS    | 201215128 |    1 |    78 |
+-----------+--------+------+------+-------+-----------+------+-------+
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扩展

如果只想从A表中取出一些记录,但不包含B表

这里写图片描述

可以在left join 后面加上一个where语句

select * from student left join sc using(Sno) where sc.Sno is null;
+-----------+-----------+------+------+-------+------+-------+
| Sno       | Sname     | Ssex | Sage | Sdept | Cno  | Grade |
+-----------+-----------+------+------+-------+------+-------+
| 201215123 | 王敏      | 女   |   18 | MA    | NULL |  NULL |
| 201215125 | 张立      | 男   |   19 | IS    | NULL |  NULL |
| 201215126 | 张成民    | 男   |   18 | CS    | NULL |  NULL |
+-----------+-----------+------+------+-------+------+-------+
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求差集

这里写图片描述

可以结合union字句,由于本例中,右侧的已经全部对应的所以显示结果,和上一个一致。

select * from student left join sc using(Sno) where student.Sno is null union 
select * from student left join sc using(Sno) where sc.Sno is null;
+-----------+-----------+------+------+-------+------+-------+
| Sno       | Sname     | Ssex | Sage | Sdept | Cno  | Grade |
+-----------+-----------+------+------+-------+------+-------+
| 201215123 | 王敏      | 女   |   18 | MA    | NULL |  NULL |
| 201215125 | 张立      | 男   |   19 | IS    | NULL |  NULL |
| 201215126 | 张成民    | 男   |   18 | CS    | NULL |  NULL |
+-----------+-----------+------+------+-------+------+-------+
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FULL JOIN

这里写图片描述

 select * from student left join sc on student.Sno=sc.Sno union  select * from student right join sc on student.Sno=sc.Sno;
+-----------+-----------+------+------+-------+-----------+------+-------+
| Sno       | Sname     | Ssex | Sage | Sdept | Sno       | Cno  | Grade |
+-----------+-----------+------+------+-------+-----------+------+-------+
| 201215121 | 李勇      | 男   |   22 | CS    | 201215121 |    1 |    92 |
| 201215121 | 李勇      | 男   |   22 | CS    | 201215121 |    2 |    85 |
| 201215121 | 李勇      | 男   |   22 | CS    | 201215121 |    3 |    88 |
| 201215122 | 刘晨      | 女   |   19 | CS    | 201215122 |    2 |    90 |
| 201215122 | 刘晨      | 女   |   19 | CS    | 201215122 |    3 |    80 |
| 201215128 | 陈冬      | 男   |   18 | IS    | 201215128 |    1 |    78 |
| 201215123 | 王敏      | 女   |   18 | MA    |      NULL | NULL |  NULL |
| 201215125 | 张立      | 男   |   19 | IS    |      NULL | NULL |  NULL |
| 201215126 | 张成民    | 男   |   18 | CS    |      NULL | NULL |  NULL |
+-----------+-----------+------+------+-------+-----------+------+-------+
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注:A left join B 等同于 B right join A

mysql> select * from student left join sc using(Sno);
+-----------+-----------+------+------+-------+------+-------+
| Sno       | Sname     | Ssex | Sage | Sdept | Cno  | Grade |
+-----------+-----------+------+------+-------+------+-------+
| 201215121 | 李勇      | 男   |   22 | CS    |    1 |    92 |
| 201215121 | 李勇      | 男   |   22 | CS    |    2 |    85 |
| 201215121 | 李勇      | 男   |   22 | CS    |    3 |    88 |
| 201215122 | 刘晨      | 女   |   19 | CS    |    2 |    90 |
| 201215122 | 刘晨      | 女   |   19 | CS    |    3 |    80 |
| 201215128 | 陈冬      | 男   |   18 | IS    |    1 |    78 |
| 201215123 | 王敏      | 女   |   18 | MA    | NULL |  NULL |
| 201215125 | 张立      | 男   |   19 | IS    | NULL |  NULL |
| 201215126 | 张成民    | 男   |   18 | CS    | NULL |  NULL |
+-----------+-----------+------+------+-------+------+-------+
9 rows in set (0.00 sec)mysql> select * from sc right join student using(Sno);
+-----------+-----------+------+------+-------+------+-------+
| Sno       | Sname     | Ssex | Sage | Sdept | Cno  | Grade |
+-----------+-----------+------+------+-------+------+-------+
| 201215121 | 李勇      | 男   |   22 | CS    |    1 |    92 |
| 201215121 | 李勇      | 男   |   22 | CS    |    2 |    85 |
| 201215121 | 李勇      | 男   |   22 | CS    |    3 |    88 |
| 201215122 | 刘晨      | 女   |   19 | CS    |    2 |    90 |
| 201215122 | 刘晨      | 女   |   19 | CS    |    3 |    80 |
| 201215128 | 陈冬      | 男   |   18 | IS    |    1 |    78 |
| 201215123 | 王敏      | 女   |   18 | MA    | NULL |  NULL |
| 201215125 | 张立      | 男   |   19 | IS    | NULL |  NULL |
| 201215126 | 张成民    | 男   |   18 | CS    | NULL |  NULL |
+-----------+-----------+------+------+-------+------+-------+
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MySQL中join用法解析

实例数据库如下:
student表:

mysql> select * from student;
+-----------+-----------+------+------+-------+
| Sno       | Sname     | Ssex | Sage | Sdept |
+-----------+-----------+------+------+-------+
| 201215121 | 李勇      | 男   |   22 | CS    |
| 201215122 | 刘晨      | 女   |   19 | CS    |
| 201215123 | 王敏      | 女   |   18 | MA    |
| 201215125 | 张立      | 男   |   19 | IS    |
| 201215128 | 陈冬      | 男   |   18 | IS    |
| 201215126 | 张成民    | 男   |   18 | CS    |
+-----------+-----------+------+------+-------+
6 rows in set (0.00 sec)
Salin selepas log masuk

sc表:

mysql> select * from sc;
+-----------+------+-------+
| Sno       | Cno  | Grade |
+-----------+------+-------+
| 201215121 |    1 |    92 |
| 201215121 |    2 |    85 |
| 201215121 |    3 |    88 |
| 201215122 |    2 |    90 |
| 201215122 |    3 |    80 |
| 201215128 |    1 |    78 |
+-----------+------+-------+
6 rows in set (0.00 sec)
Salin selepas log masuk

LEFT JOIN(左连接)

这里写图片描述
sql语句如下:

select * from student left join sc on student.Sno=sc.Sno;
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运行结果如下:

+-----------+-----------+------+------+-------+-----------+------+-------+
| Sno       | Sname     | Ssex | Sage | Sdept | Sno       | Cno  | Grade |
+-----------+-----------+------+------+-------+-----------+------+-------+
| 201215121 | 李勇      | 男   |   22 | CS    | 201215121 |    1 |    92 |
| 201215121 | 李勇      | 男   |   22 | CS    | 201215121 |    2 |    85 |
| 201215121 | 李勇      | 男   |   22 | CS    | 201215121 |    3 |    88 |
| 201215122 | 刘晨      | 女   |   19 | CS    | 201215122 |    2 |    90 |
| 201215122 | 刘晨      | 女   |   19 | CS    | 201215122 |    3 |    80 |
| 201215128 | 陈冬      | 男   |   18 | IS    | 201215128 |    1 |    78 |
| 201215123 | 王敏      | 女   |   18 | MA    |      NULL | NULL |  NULL |
| 201215125 | 张立      | 男   |   19 | IS    |      NULL | NULL |  NULL |
| 201215126 | 张成民    | 男   |   18 | CS    |      NULL | NULL |  NULL |
+-----------+-----------+------+------+-------+-----------+------+-------+
Salin selepas log masuk
Salin selepas log masuk

在此例中left join 是以student表中的记录为基础,student表可以看成左表,sc表可以看成右表,左表中的记录会完全显示出来,加上匹配到的右表,如果左边没有匹配到,则其余部分显示为null。

USING字句

using字句和on字句,类似,但结果略有不同。
例如:

mysql> select student.Sno,Sname,Grade from student left join sc on student.Sno=sc.Sno;
+-----------+-----------+-------+| Sno       | Sname     | Grade |
+-----------+-----------+-------+| 201215121 | 李勇      |    92 |
| 201215121 | 李勇      |    85 |
| 201215121 | 李勇      |    88 |
| 201215122 | 刘晨      |    90 |
| 201215122 | 刘晨      |    80 |
| 201215128 | 陈冬      |    78 |
| 201215123 | 王敏      |  NULL |
| 201215125 | 张立      |  NULL || 201215126 | 张成民    |  NULL |
+-----------+-----------+-------+9 rows in set (0.00 sec)
Salin selepas log masuk

以上等价于

select Sno,Sname,Grade from student left join sc using(Sno);
+-----------+-----------+-------+| Sno       | Sname     | Grade |
+-----------+-----------+-------+| 201215121 | 李勇      |    92 |
| 201215121 | 李勇      |    85 |
| 201215121 | 李勇      |    88 |
| 201215122 | 刘晨      |    90 |
| 201215122 | 刘晨      |    80 |
| 201215128 | 陈冬      |    78 |
| 201215123 | 王敏      |  NULL |
| 201215125 | 张立      |  NULL || 201215126 | 张成民    |  NULL |
+-----------+-----------+-------+
Salin selepas log masuk

不同的地方,例如:

select * from student left join sc on student.Sno=sc.Sno;
+-----------+-----------+------+------+-------+-----------+------+-------+
| Sno       | Sname     | Ssex | Sage | Sdept | Sno       | Cno  | Grade |
+-----------+-----------+------+------+-------+-----------+------+-------+
| 201215121 | 李勇      | 男   |   22 | CS    | 201215121 |    1 |    92 |
| 201215121 | 李勇      | 男   |   22 | CS    | 201215121 |    2 |    85 |
| 201215121 | 李勇      | 男   |   22 | CS    | 201215121 |    3 |    88 |
| 201215122 | 刘晨      | 女   |   19 | CS    | 201215122 |    2 |    90 |
| 201215122 | 刘晨      | 女   |   19 | CS    | 201215122 |    3 |    80 |
| 201215128 | 陈冬      | 男   |   18 | IS    | 201215128 |    1 |    78 |
| 201215123 | 王敏      | 女   |   18 | MA    |      NULL | NULL |  NULL |
| 201215125 | 张立      | 男   |   19 | IS    |      NULL | NULL |  NULL |
| 201215126 | 张成民    | 男   |   18 | CS    |      NULL | NULL |  NULL |
+-----------+-----------+------+------+-------+-----------+------+-------+
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select * from student left join sc using (sno);
+-----------+-----------+------+------+-------+------+-------+
| Sno       | Sname     | Ssex | Sage | Sdept | Cno  | Grade |
+-----------+-----------+------+------+-------+------+-------+
| 201215121 | 李勇      | 男   |   22 | CS    |    1 |    92 |
| 201215121 | 李勇      | 男   |   22 | CS    |    2 |    85 |
| 201215121 | 李勇      | 男   |   22 | CS    |    3 |    88 |
| 201215122 | 刘晨      | 女   |   19 | CS    |    2 |    90 |
| 201215122 | 刘晨      | 女   |   19 | CS    |    3 |    80 |
| 201215128 | 陈冬      | 男   |   18 | IS    |    1 |    78 |
| 201215123 | 王敏      | 女   |   18 | MA    | NULL |  NULL |
| 201215125 | 张立      | 男   |   19 | IS    | NULL |  NULL |
| 201215126 | 张成民    | 男   |   18 | CS    | NULL |  NULL |
+-----------+-----------+------+------+-------+------+-------+
Salin selepas log masuk
Salin selepas log masuk

重复的Sno列,如果用on字句会被输出两次

RIGHT JOIN(右连接)

同LEFT JOIN,只不过以右表为基础,例如:

 select * from student right join sc using (sno);
+-----------+------+-------+--------+------+------+-------+
| Sno       | Cno  | Grade | Sname  | Ssex | Sage | Sdept |
+-----------+------+-------+--------+------+------+-------+
| 201215121 |    1 |    92 | 李勇   | 男   |   22 | CS    |
| 201215121 |    2 |    85 | 李勇   | 男   |   22 | CS    |
| 201215121 |    3 |    88 | 李勇   | 男   |   22 | CS    |
| 201215122 |    2 |    90 | 刘晨   | 女   |   19 | CS    |
| 201215122 |    3 |    80 | 刘晨   | 女   |   19 | CS    |
| 201215128 |    1 |    78 | 陈冬   | 男   |   18 | IS    |
+-----------+------+-------+--------+------+------+-------+
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INNER JOIN(相等连接或内连接)

这里写图片描述

不会显示以谁为基础,只会显示符合条件的记录

 select * from student inner join sc on student.Sno=sc.Sno;
+-----------+--------+------+------+-------+-----------+------+-------+
| Sno       | Sname  | Ssex | Sage | Sdept | Sno       | Cno  | Grade |
+-----------+--------+------+------+-------+-----------+------+-------+
| 201215121 | 李勇   | 男   |   22 | CS    | 201215121 |    1 |    92 |
| 201215121 | 李勇   | 男   |   22 | CS    | 201215121 |    2 |    85 |
| 201215121 | 李勇   | 男   |   22 | CS    | 201215121 |    3 |    88 |
| 201215122 | 刘晨   | 女   |   19 | CS    | 201215122 |    2 |    90 |
| 201215122 | 刘晨   | 女   |   19 | CS    | 201215122 |    3 |    80 |
| 201215128 | 陈冬   | 男   |   18 | IS    | 201215128 |    1 |    78 |
+-----------+--------+------+------+-------+-----------+------+-------+
Salin selepas log masuk
Salin selepas log masuk

以上语句等同于:

select * from student,sc where student.Sno=sc.Sno;
+-----------+--------+------+------+-------+-----------+------+-------+
| Sno       | Sname  | Ssex | Sage | Sdept | Sno       | Cno  | Grade |
+-----------+--------+------+------+-------+-----------+------+-------+
| 201215121 | 李勇   | 男   |   22 | CS    | 201215121 |    1 |    92 |
| 201215121 | 李勇   | 男   |   22 | CS    | 201215121 |    2 |    85 |
| 201215121 | 李勇   | 男   |   22 | CS    | 201215121 |    3 |    88 |
| 201215122 | 刘晨   | 女   |   19 | CS    | 201215122 |    2 |    90 |
| 201215122 | 刘晨   | 女   |   19 | CS    | 201215122 |    3 |    80 |
| 201215128 | 陈冬   | 男   |   18 | IS    | 201215128 |    1 |    78 |
+-----------+--------+------+------+-------+-----------+------+-------+
Salin selepas log masuk
Salin selepas log masuk

扩展

如果只想从A表中取出一些记录,但不包含B表

这里写图片描述

可以在left join 后面加上一个where语句

select * from student left join sc using(Sno) where sc.Sno is null;
+-----------+-----------+------+------+-------+------+-------+
| Sno       | Sname     | Ssex | Sage | Sdept | Cno  | Grade |
+-----------+-----------+------+------+-------+------+-------+
| 201215123 | 王敏      | 女   |   18 | MA    | NULL |  NULL |
| 201215125 | 张立      | 男   |   19 | IS    | NULL |  NULL |
| 201215126 | 张成民    | 男   |   18 | CS    | NULL |  NULL |
+-----------+-----------+------+------+-------+------+-------+
Salin selepas log masuk
Salin selepas log masuk

求差集

这里写图片描述

可以结合union字句,由于本例中,右侧的已经全部对应的所以显示结果,和上一个一致。

select * from student left join sc using(Sno) where student.Sno is null union 
select * from student left join sc using(Sno) where sc.Sno is null;
+-----------+-----------+------+------+-------+------+-------+
| Sno       | Sname     | Ssex | Sage | Sdept | Cno  | Grade |
+-----------+-----------+------+------+-------+------+-------+
| 201215123 | 王敏      | 女   |   18 | MA    | NULL |  NULL |
| 201215125 | 张立      | 男   |   19 | IS    | NULL |  NULL |
| 201215126 | 张成民    | 男   |   18 | CS    | NULL |  NULL |
+-----------+-----------+------+------+-------+------+-------+
Salin selepas log masuk
Salin selepas log masuk

FULL JOIN

这里写图片描述

 select * from student left join sc on student.Sno=sc.Sno union  select * from student right join sc on student.Sno=sc.Sno;
+-----------+-----------+------+------+-------+-----------+------+-------+
| Sno       | Sname     | Ssex | Sage | Sdept | Sno       | Cno  | Grade |
+-----------+-----------+------+------+-------+-----------+------+-------+
| 201215121 | 李勇      | 男   |   22 | CS    | 201215121 |    1 |    92 |
| 201215121 | 李勇      | 男   |   22 | CS    | 201215121 |    2 |    85 |
| 201215121 | 李勇      | 男   |   22 | CS    | 201215121 |    3 |    88 |
| 201215122 | 刘晨      | 女   |   19 | CS    | 201215122 |    2 |    90 |
| 201215122 | 刘晨      | 女   |   19 | CS    | 201215122 |    3 |    80 |
| 201215128 | 陈冬      | 男   |   18 | IS    | 201215128 |    1 |    78 |
| 201215123 | 王敏      | 女   |   18 | MA    |      NULL | NULL |  NULL |
| 201215125 | 张立      | 男   |   19 | IS    |      NULL | NULL |  NULL |
| 201215126 | 张成民    | 男   |   18 | CS    |      NULL | NULL |  NULL |
+-----------+-----------+------+------+-------+-----------+------+-------+
Salin selepas log masuk
Salin selepas log masuk

注:A left join B 等同于 B right join A

mysql> select * from student left join sc using(Sno);
+-----------+-----------+------+------+-------+------+-------+
| Sno       | Sname     | Ssex | Sage | Sdept | Cno  | Grade |
+-----------+-----------+------+------+-------+------+-------+
| 201215121 | 李勇      | 男   |   22 | CS    |    1 |    92 |
| 201215121 | 李勇      | 男   |   22 | CS    |    2 |    85 |
| 201215121 | 李勇      | 男   |   22 | CS    |    3 |    88 |
| 201215122 | 刘晨      | 女   |   19 | CS    |    2 |    90 |
| 201215122 | 刘晨      | 女   |   19 | CS    |    3 |    80 |
| 201215128 | 陈冬      | 男   |   18 | IS    |    1 |    78 |
| 201215123 | 王敏      | 女   |   18 | MA    | NULL |  NULL |
| 201215125 | 张立      | 男   |   19 | IS    | NULL |  NULL |
| 201215126 | 张成民    | 男   |   18 | CS    | NULL |  NULL |
+-----------+-----------+------+------+-------+------+-------+
9 rows in set (0.00 sec)mysql> select * from sc right join student using(Sno);
+-----------+-----------+------+------+-------+------+-------+
| Sno       | Sname     | Ssex | Sage | Sdept | Cno  | Grade |
+-----------+-----------+------+------+-------+------+-------+
| 201215121 | 李勇      | 男   |   22 | CS    |    1 |    92 |
| 201215121 | 李勇      | 男   |   22 | CS    |    2 |    85 |
| 201215121 | 李勇      | 男   |   22 | CS    |    3 |    88 |
| 201215122 | 刘晨      | 女   |   19 | CS    |    2 |    90 |
| 201215122 | 刘晨      | 女   |   19 | CS    |    3 |    80 |
| 201215128 | 陈冬      | 男   |   18 | IS    |    1 |    78 |
| 201215123 | 王敏      | 女   |   18 | MA    | NULL |  NULL |
| 201215125 | 张立      | 男   |   19 | IS    | NULL |  NULL |
| 201215126 | 张成民    | 男   |   18 | CS    | NULL |  NULL |
+-----------+-----------+------+------+-------+------+-------+
Salin selepas log masuk
Salin selepas log masuk

 以上就是MySQL中join用法解析的内容,更多相关内容请关注PHP中文网(m.sbmmt.com)!


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