如何仅从一个MySQL列中选择不同的值？
要仅从一列中选择不同的值，可以将聚合函数MAX()与GROUPBY一起使用。让我们首先创建一个表-
mysql> create table distinctFromOneColumn -> ( -> StudentId int, -> StudentName varchar(100) -> );
以下是使用insert命令在表中插入记录的查询-
mysql> insert into distinctFromOneColumn values(1001,'John'); mysql> insert into distinctFromOneColumn values(1002,'Carol'); mysql> insert into distinctFromOneColumn values(1001,'Sam'); mysql> insert into distinctFromOneColumn values(1001,'David'); mysql> insert into distinctFromOneColumn values(1002,'Ramit'); mysql> insert into distinctFromOneColumn values(1003,'Bob');
以下是使用select语句显示表中所有记录的查询-
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)
这是仅从一列中选择唯一值的查询-
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)