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如何计算MySQL数据库中一列的唯一记录？

2024-05-14 14:11:08 499

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)

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如何计算MySQL数据库中一列的唯一记录？

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