MySQL中的RAND()函数使用详解

MySQL RAND()函数调用可以在0和1之间产生一个随机数：

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

当调用一个整数参数时，RAND()使用该随机数发生器种子值。每次在给定值种子生成，RAND()会产生一个可重复的一系列数字：

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

可以使用ORDER BY RAND()，随机组行或值如下：

要了解ORDER BY RAND()函数, 假设EMPLOYEE_TBL的表有以下记录：

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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)

现在使用以下目录：

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