MySQL 如何进行分组但随机排序？

让我们首先创建一个表 –

mysql> create table DemoTable (
   Id int NOT NULL AUTO_INCREMENT PRIMARY KEY,
   Value char(1)
   );
Query OK, 0 rows affected (0.66 sec)

使用插入语句将一些记录插入表中 –

mysql> insert into DemoTable(Value) values('X');
Query OK, 1 row affected (0.20 sec)

mysql> insert into DemoTable(Value) values('Y');
Query OK, 1 row affected (0.09 sec)

mysql> insert into DemoTable(Value) values('X');
Query OK, 1 row affected (0.30 sec)

mysql> insert into DemoTable(Value) values('X');
Query OK, 1 row affected (0.07 sec)

mysql> insert into DemoTable(Value) values('Y');
Query OK, 1 row affected (0.17 sec)

mysql> insert into DemoTable(Value) values('Z');
Query OK, 1 row affected (0.13 sec)

mysql> insert into DemoTable(Value) values('Z');
Query OK, 1 row affected (0.11 sec)

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 –

+----+-------+
| Id | Value |
+----+-------+
| 1  | X     |
| 2  | Y     |
| 3  | X     |
| 4  | X     |
| 5  | Y     |
| 6  | Z     |
| 7  | Z     |
+----+-------+
7 rows in set (0.00 sec)

Case 1

- 以下是执行分组但随机排序的查询 –

mysql> select DemoTable.*
   from DemoTable join
   (
   select Value, rand() as `random_Value`
   from DemoTable
   group by Value
   ) tbl2
   on DemoTable.Value = tbl2.Value
order by tbl2.`random_Value`;

这将产生以下输出 –

+----+-------+
| Id | Value |
+----+-------+
| 6  | Z     |
| 7  | Z     |
| 1  | X     |
| 3  | X     |
| 4  | X     |
| 2  | Y     |
| 5  | Y     |
+----+-------+
7 rows in set (0.00 sec)

Case 2

- 让我们再次运行上面的查询以显示随机记录 –

mysql> select DemoTable.*
   from DemoTable join
   (
   select Value, rand() as `random_Value`
   from DemoTable
   group by Value
   ) tbl2
   on DemoTable.Value = tbl2.Value
order by tbl2.`random_Value`;

这将产生以下输出 –

+----+-------+
| Id | Value |
+----+-------+
| 2  | Y     |
| 5  | Y     |
| 6  | Z     |
| 7  | Z     |
| 1  | X     |
| 3  | X     |
| 4  | X     |
+----+-------+
7 rows in set (0.00 sec)

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