MySQL GROUP BY date when using datetime?

To GROUP BY date while using datetime, the following is the syntax −

select *from yourTableName GROUP BY date(yourColumnName);

To understand the above syntax, let us create a table. The query to create a table is as follows −

mysql> create table groupByDateDemo
   -> (
   -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY,
   -> UserName varchar(20),
   -> UserPostDatetime datetime
   -> );
Query OK, 0 rows affected (0.53 sec)

Insert some records in the table using insert command. The query is as follows −

mysql> insert into groupByDateDemo(UserName,UserPostDatetime) values('Larry','2018-01-02 13:45:40');
Query OK, 1 row affected (0.18 sec)
mysql> insert into groupByDateDemo(UserName,UserPostDatetime) values('Mike','2018-01-02 13:45:40');
Query OK, 1 row affected (0.14 sec)
mysql> insert into groupByDateDemo(UserName,UserPostDatetime) values('Sam','2019-01-28 12:30:34');
Query OK, 1 row affected (0.33 sec)
mysql> insert into groupByDateDemo(UserName,UserPostDatetime) values('David','2019-02-10 11:35:54');
Query OK, 1 row affected (0.18 sec)
mysql> insert into groupByDateDemo(UserName,UserPostDatetime) values('Maxwell','2019-02-10 11:35:54');
Query OK, 1 row affected (0.21 sec)

Display all records from the table using select statement. The query is as follows −

mysql> select *from groupByDateDemo;

Here is the output −

+----+----------+---------------------+
| 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)

Let us now GROUP BY date while using datetime. The query is as follows −

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

The following is the output −

+----+----------+---------------------+
| 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)