Query was empty. Where is the mistake?

I can not, care today is asleep. Help

$username="root"; $passwd=""; $hostname="localhost"; $basename="azbuka"; $db_conect=mysql_connect($hostname,$username,$passwd) or die ("Ошибка, нет доступа к базе"); mysql_select_db($basename,$db_conect); $SQL="SELECT id_web,name,address,city FROM markets where y_precision is NULL"; $TData=mysql_query($sql) or die (mysql_error());