如何计算MySQL数据库中一列的唯一记录？
为此，使用聚合函数count（*）计数到GROUPBY进行分组。让我们首先创建一个表-
mysql> create table DemoTable ( UserName varchar(100), UserPostMessage text );
使用插入命令在表中插入一些记录-
mysql> insert into DemoTable values('Chris','Hi');
mysql> insert into DemoTable values('David','Hello');
mysql> insert into DemoTable values('Chris','Awesome');
mysql> insert into DemoTable values('Chris','Amazing');
mysql> insert into DemoTable values('David','Nice Place');
mysql> insert into DemoTable values('Chris','Amazing');使用select语句显示表中的所有记录-
mysql> select *from DemoTable;
这将产生以下输出-
+----------+-----------------+ | UserName | UserPostMessage | +----------+-----------------+ | Chris | Hi | | David | Hello | | Chris | Awesome | | Chris | Amazing | | David | Nice Place | | Chris | Amazing | +----------+-----------------+ 6 rows in set (0.00 sec)
这是查询以对我的MySQL数据库中的列进行唯一记录计数的查询-
mysql> select UserName,count(DISTINCT UserPostMessage) AS NumberOfMessagesPostByUser from DemoTable group by UserName;
这将产生以下输出-
+----------+----------------------------+ | UserName | NumberOfMessagesPostByUser | +----------+----------------------------+ | Chris | 3 | | David | 2 | +----------+----------------------------+ 2 rows in set (0.00 sec)