如何从MySQL的一列中选择不同的值？

为了从一个列中选择唯一的值，可以使用MAX()和GROUP BY聚合函数。让我们首先创建一个表 –

mysql> create table distinctFromOneColumn
    -> (
    -> StudentId int,
    -> StudentName varchar(100)
    -> );
Query OK, 0 rows affected (0.77 sec)

接下来使用insert命令向表中插入记录，如下所示 –

mysql> insert into distinctFromOneColumn values(1001,'John');
Query OK, 1 row affected (0.15 sec)

mysql> insert into distinctFromOneColumn values(1002,'Carol');
Query OK, 1 row affected (0.15 sec)

mysql> insert into distinctFromOneColumn values(1001,'Sam');
Query OK, 1 row affected (0.15 sec)

mysql> insert into distinctFromOneColumn values(1001,'David');
Query OK, 1 row affected (0.16 sec)

mysql> insert into distinctFromOneColumn values(1002,'Ramit');
Query OK, 1 row affected (0.15 sec)

mysql> insert into distinctFromOneColumn values(1003,'Bob');
Query OK, 1 row affected (0.21 sec)

以下是使用SELECT语句从表中显示所有记录的查询 –

mysql> select * from distinctFromOneColumn;

这将产生以下输出 –

+-----------+-------------+
| StudentId | StudentName |
+-----------+-------------+
| 1001      | John        |
| 1002      | Carol       |
| 1001      | Sam         |
| 1001      | David       |
| 1002      | Ramit       |
| 1003      | Bob         |
+-----------+-------------+
6 rows in set (0.00 sec)

以下是从一个列中选择不同值的查询 –

mysql> select StudentId,MAX(StudentName) AS StudentName
    -> from distinctFromOneColumn
    -> group by StudentId;

这将产生以下输出 –

+-----------+-------------+
| StudentId | StudentName |
+-----------+-------------+
| 1001      | Sam         |
| 1002      | Ramit       |
| 1003      | Bob         |
+-----------+-------------+
3 rows in set (0.00 sec)

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