Strange select results when running this query "select * FROM tmp WHERE id in (select cast(rand()*10 as int)+1);" against a simple small table.

This is easy enough to reproduce:

CREATE TABLE `tmp` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`id_user` int(10) unsigned DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=16 DEFAULT CHARSET=utf8;

INSERT INTO `tmp` VALUES (1,80),(2,253),(3,333),(4,569),(5,606),(6,618),(7,660),(8,663),(9,690),(10,693);

select * FROM tmp WHERE id in (select cast(rand()*10 as int)+1);
Empty set (0.001 sec)

select * FROM tmp WHERE id in (select cast(rand()*10 as int)+1);
-----------+

-----------+

-----------+
2 rows in set (0.001 sec)
select * FROM tmp WHERE id in (select cast(rand()*10 as int)+1);
-----------+

-----------+

-----------+
4 rows in set (0.000 sec)

but when I run select cast(rand()*10 as int)+1 alone, I only ever get one result...