MySQL中的RAND()函数使用详解
2024-08-30 13:01:30
转自:https://www.jb51.net/article/66697.htm
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) |
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