[PrawkC]

Код:

ExistingAccount(playerid) //Check to see if the account is already registered.
{
	new query[124];
	format(query, sizeof(query), "SELECT * FROM accts WHERE username = '%s'", getName(playerid));
	mysql_query(query);
	mysql_store_result();
	
	if(mysql_num_rows() > 0)
	{
		mysql_free_result();
		return 1;	
	}
	mysql_free_result();	
	return 0;
}

You're going to have to set query to yours, and also I didn't do any string escaping, as this is from an old script but see above how to do so