MySQL - Función RAND

MySQL tiene una RAND función que se puede invocar para producir números aleatorios entre 0 y 1 -

mysql>  SELECT RAND( ), RAND( ), RAND( );
+------------------+-----------------+------------------+
|      RAND( )     |      RAND( )    |      RAND( )     |
+------------------+-----------------+------------------+
| 0.45464584925645 | 0.1824410643265 | 0.54826780459682 |
+------------------+-----------------+------------------+
1 row in set (0.00 sec)

Cuando se invoca con un argumento entero, RAND () usa ese valor para inicializar el generador de números aleatorios. Cada vez que siembra el generador con un valor dado, RAND () producirá una serie repetible de números:

mysql>  SELECT RAND(1), RAND( ), RAND( );
+------------------+------------------+------------------+
|     RAND(1 )     |      RAND( )     |      RAND( )     |
+------------------+------------------+------------------+
| 0.18109050223705 | 0.75023211143001 | 0.20788908117254 |
+------------------+------------------+------------------+
1 row in set (0.00 sec)

Puedes usar ORDER BY RAND() para aleatorizar un conjunto de filas o valores de la siguiente manera:

Comprender ORDER BY RAND() función, considere una employee_tbl tabla, que tiene los siguientes registros:

mysql> SELECT * FROM employee_tbl;
+------+------+------------+--------------------+
|  id  | name | work_date  | daily_typing_pages |
+------+------+------------+--------------------+
|   1  | John | 2007-01-24 |        250         |
|   2  | Ram  | 2007-05-27 |        220         |
|   3  | Jack | 2007-05-06 |        170         |
|   3  | Jack | 2007-04-06 |        100         |
|   4  | Jill | 2007-04-06 |        220         |
|   5  | Zara | 2007-06-06 |        300         |
|   5  | Zara | 2007-02-06 |        350         |
+------+------+------------+--------------------+
7 rows in set (0.00 sec)

Ahora, use los siguientes comandos:

mysql> SELECT * FROM employee_tbl ORDER BY RAND();
+------+------+------------+--------------------+
|  id  | name | work_date  | daily_typing_pages |
+------+------+------------+--------------------+
|   5  | Zara | 2007-02-06 |        350         |
|   5  | Zara | 2007-06-06 |        300         |
|   3  | Jack | 2007-05-06 |        170         |
|   2  | Ram  | 2007-05-27 |        220         |
|   4  | Jill | 2007-04-06 |        220         |
|   5  | Zara | 2007-02-06 |        350         |
|   1  | John | 2007-01-24 |        250         |
+------+------+------------+--------------------+
7 rows in set (0.01 sec)

mysql> SELECT * FROM employee_tbl ORDER BY RAND();
+------+------+------------+--------------------+
|  id  | name | work_date  | daily_typing_pages |
+------+------+------------+--------------------+
|   5  | Zara | 2007-02-06 |        350         |
|   5  | Zara | 2007-06-06 |        300         |
|   3  | Jack | 2007-05-06 |        170         |
|   2  | Ram  | 2007-05-27 |        220         |
|   4  | Jill | 2007-04-06 |        220         |
|   5  | Zara | 2007-02-06 |        350         |
|   1  | John | 2007-01-24 |        250         |
+------+------+------------+--------------------+
7 rows in set (0.00 sec)