MySQL Cookbook

Generating Random Numbers

Problem

You need a source of random numbers.

Solution

Invoke MySQL’s RAND( ) function.

Discussion

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( )           |
+------------------+------------------+------------------+
| 0.31466114177803 | 0.89354679723601 | 0.52375059157959 |
+------------------+------------------+------------------+

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 |
+------------------+------------------+------------------+
mysql> SELECT RAND(20000000), RAND( ), RAND( );
+------------------+-------------------+------------------+
| RAND(20000000)   | RAND( )            | RAND( )           |
+------------------+-------------------+------------------+
| 0.24628307879556 | 0.020315642487552 | 0.36272900678472 |
+------------------+-------------------+------------------+
mysql> SELECT RAND(1), RAND( ), RAND( ); +------------------+------------------+------------------+ | RAND(1) | RAND( ) | RAND( ) | +------------------+------------------+------------------+ ...