MySQL - RAND Function


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MySQL has a RAND function that can be invoked to produce random numbers between 0 and 1 −

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

When invoked with an integer argument, RAND( ) uses that value to seed the random number generator. Each time you seed the generator with a given value, RAND( ) will produce a repeatable series of numbers −

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

You can use ORDER BY RAND() to randomize a set of rows or values as follows −

To understand ORDER BY RAND() function, consider an employee_tbl table, which is having the following records −

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)

Now, use the following commands −

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)

mysql-useful-functions.htm

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