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)
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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)
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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)
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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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