mysql rand()函数调用可以在0和1之间产生一个随机数:
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:
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:
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:
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)
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