MySQL RAND 函数

RAND 函数

MySQL RAND函数，可以调用该函数以产生0到1之间的随机数-

mysql>  SELECT RAND( ), RAND( ), RAND( );
+------------------+-----------------+------------------+
|      RAND( )     |      RAND( )    |      RAND( )     |
+------------------+-----------------+------------------+
| 0.45464584825645 | 0.1824410643165 | 0.54826780759682 |
+------------------+-----------------+------------------+
1 row in set (0.00 sec)

当使用整数参数调用时，RAND()使用该值作为随机数生成器的种子。每次使用给定值为生成器提供种子时，RAND()都会产生一系列可重复的数字-

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

您可以使用ORDER BY RAND()将一组行或值随机化，如下所示 - 要了解ORDER BY RAND()函数，请考虑一个employee_tbl表，该表具有以下记录-

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)

现在，使用以下命令

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)