zerofill

php -r "echo str_pad(15, 6, '0', STR_PAD_LEFT);"
000015

php -r "echo str_pad(999999, 6, '0', STR_PAD_LEFT);"
999999

MySQL
Table: game
Field: code - Type: int(6) unsigned zerofill

SELECT * FROM game WHERE code=5;
same
SELECT * FROM game WHERE code='000005';
even
SELECT * FROM game WHERE code='00000000005';
or
SELECT * FROM game WHERE code='05';

So you don't worry about...