MySQL中join用法解析
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2022-03-28 15:12:56
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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)
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)
LEFT JOIN（左连接）
sql语句如下：
select * from student left join sc on student.Sno=sc.Sno;
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 | +-----------+-----------+------+------+-------+-----------+------+-------+
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)
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 | +-----------+-----------+-------+
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 | +-----------+-----------+------+------+-------+-----------+------+-------+
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 | +-----------+-----------+------+------+-------+------+-------+
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 | +-----------+------+-------+--------+------+------+-------+
INNER JOIN（相等连接或内连接）
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 | +-----------+--------+------+------+-------+-----------+------+-------+
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 | +-----------+--------+------+------+-------+-----------+------+-------+
扩展
如果只想从A表中取出一些记录，但不包含B表
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 | +-----------+-----------+------+------+-------+------+-------+
求差集
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 | +-----------+-----------+------+------+-------+------+-------+
FULL JOIN
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 | +-----------+-----------+------+------+-------+-----------+------+-------+
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 | +-----------+-----------+------+------+-------+------+-------+
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)
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)
LEFT JOIN（左连接）
sql语句如下：
select * from student left join sc on student.Sno=sc.Sno;
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 | +-----------+-----------+------+------+-------+-----------+------+-------+
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)
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 | +-----------+-----------+-------+
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 | +-----------+-----------+------+------+-------+-----------+------+-------+
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 | +-----------+-----------+------+------+-------+------+-------+
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 | +-----------+------+-------+--------+------+------+-------+
INNER JOIN（相等连接或内连接）
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 | +-----------+--------+------+------+-------+-----------+------+-------+
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 | +-----------+--------+------+------+-------+-----------+------+-------+
扩展
如果只想从A表中取出一些记录，但不包含B表
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 | +-----------+-----------+------+------+-------+------+-------+
求差集
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 | +-----------+-----------+------+------+-------+------+-------+
FULL JOIN
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 | +-----------+-----------+------+------+-------+-----------+------+-------+
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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