GROUP BY จำนวนแถวที่ GROUP BY คืนค่าใน MySQL

ใช้ GROUP_CONCAT() เพื่อจัดกลุ่มตามจำนวนแถว สร้างตาราง:

mysql> create table groupByDemo
    -> (
    -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY,
    -> Name varchar(100)
    -> );
Query OK, 0 rows affected (1.31 sec)

เพิ่มข้อมูล:

mysql> insert into groupByDemo(Name) values('John');
Query OK, 1 row affected (0.19 sec)
mysql> insert into groupByDemo(Name) values('Carol');
Query OK, 1 row affected (0.14 sec)
mysql> insert into groupByDemo(Name) values('Carol');
Query OK, 1 row affected (0.10 sec)
mysql> insert into groupByDemo(Name) values('Bob');
Query OK, 1 row affected (0.24 sec)
mysql> insert into groupByDemo(Name) values('Bob');
Query OK, 1 row affected (0.23 sec)
mysql> insert into groupByDemo(Name) values('Bob');
Query OK, 1 row affected (0.17 sec)
mysql> insert into groupByDemo(Name) values('John');
Query OK, 1 row affected (0.16 sec)
mysql> insert into groupByDemo(Name) values('John');
Query OK, 1 row affected (0.07 sec)
mysql> insert into groupByDemo(Name) values('John');
Query OK, 1 row affected (0.11 sec)
mysql> insert into groupByDemo(Name) values('Sam');
Query OK, 1 row affected (0.17 sec)
mysql> insert into groupByDemo(Name) values('Carol');
Query OK, 1 row affected (0.19 sec)

แสดงข้อมูล:

mysql> select * from groupByDemo;

+----+-------+
| Id | Name  |
+----+-------+
| 1  | John  |
| 2  | Carol |
| 3  | Carol |
| 4  | Bob   |
| 5  | Bob   |
| 6  | Bob   |
| 7  | John  |
| 8  | John  |
| 9  | John  |
| 10 | Sam   |
| 11 | Carol |
+----+-------+
11 rows in set (0.00 sec)

คำสั่ง GROUP BY จำนวนแถว:

mysql> SELECT Counter, GROUP_CONCAT(Name SEPARATOR ', ') as AllName
    -> FROM (SELECT Name, COUNT(Name) as Counter
    -> FROM groupByDemo
    -> GROUP BY Name) tbl
    -> GROUP BY Counter
    -> ORDER BY Counter DESC;

+---------+------------+
| Counter | AllName    |
+---------+------------+
| 4       | John       |
| 3       | Carol, Bob |
| 1       | Sam        |
+---------+------------+
3 rows in set (0.00 sec)