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MySQL GROUP BY使用datetime时的日期？

2024-04-28 18:15:03 524

要在使用datetime时使用GROUPBYdate，以下是语法-

select *from yourTableName GROUP BY date(yourColumnName);

为了理解上述语法，让我们创建一个表。创建表的查询如下-

mysql> create table groupByDateDemo
   -> (
   -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY,
   -> UserName varchar(20),
   -> UserPostDatetime datetime
   -> );

使用insert命令在表中插入一些记录。查询如下-

mysql> insert into groupByDateDemo(UserName,UserPostDatetime) values('Larry','2018-01-02 13:45:40');
mysql> insert into groupByDateDemo(UserName,UserPostDatetime) values('Mike','2018-01-02 13:45:40');
mysql> insert into groupByDateDemo(UserName,UserPostDatetime) values('Sam','2019-01-28 12:30:34');
mysql> insert into groupByDateDemo(UserName,UserPostDatetime) values('David','2019-02-10 11:35:54');
mysql> insert into groupByDateDemo(UserName,UserPostDatetime) values('Maxwell','2019-02-10 11:35:54');

使用select语句显示表中的所有记录。查询如下-

mysql> select *from groupByDateDemo;

这是输出-

+----+----------+---------------------+
| Id | UserName | UserPostDatetime    |
+----+----------+---------------------+
| 1  | Larry    | 2018-01-02 13:45:40 |
| 2  | Mike     | 2018-01-02 13:45:40 |
| 3  | Sam      | 2019-01-28 12:30:34 |
| 4  | David    | 2019-02-10 11:35:54 |
| 5  | Maxwell  | 2019-02-10 11:35:54 |
+----+----------+---------------------+
5 rows in set (0.00 sec)

现在让我们在使用datetime时按日期分组。查询如下-

mysql> select *from groupByDateDemo GROUP BY date(UserPostDatetime);

以下是输出-

+----+----------+---------------------+
| Id | UserName | UserPostDatetime    |
+----+----------+---------------------+
| 1  | Larry    | 2018-01-02 13:45:40 |
| 3  | Sam      | 2019-01-28 12:30:34 |
| 4  | David    | 2019-02-10 11:35:54 |
+----+----------+---------------------+
3 rows in set (0.00 sec)

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MySQL GROUP BY使用datetime时的日期？

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