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法学如何在 MySQL GROUP BY 子句中对行进行排序或选择？
让我们先创建一个表 -
mysql> create table DemoTable1572 -> ( -> StudentId int, -> StudentMarks int, -> StudentName varchar(20) -> ); Query OK, 0 rows affected (0.56 sec)
使用以下插入命令向表中插入一些记录 -
mysql> insert into DemoTable1572 values(1,79,'Sam'); Query OK, 1 row affected (0.10 sec) mysql> insert into DemoTable1572 values(2,89,'Chris'); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable1572 values(3,98,'David'); Query OK, 1 row affected (0.22 sec) mysql> insert into DemoTable1572 values(4,79,'Bob'); Query OK, 1 row affected (0.10 sec)
使用 select 语句从表中显示所有记录 -
mysql> select * from DemoTable1572;
这将产生以下输出 -
+-----------+--------------+-------------+ | StudentId | StudentMarks | StudentName | +-----------+--------------+-------------+ | 1 | 79 | Sam | | 2 | 89 | Chris | | 3 | 98 | David | | 4 | 79 | Bob | +-----------+--------------+-------------+ 4 rows in set (0.00 sec)
以下是在 MySQL GROUP BY 子句中对行进行排序或选择的查询 -
mysql> select * from DemoTable1572 -> where StudentId in (select min(StudentId) from DemoTable1572 group by StudentMarks);
这将产生以下输出 -
+-----------+--------------+-------------+ | StudentId | StudentMarks | StudentName | +-----------+--------------+-------------+ | 1 | 79 | Sam | | 2 | 89 | Chris | | 3 | 98 | David | +-----------+--------------+-------------+ 3 rows in set (0.10 sec)
更新于：16-12-2019
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