help how to DELETE some tables..

i have some select code:

$query20 =
"SELECT * FROM `product_group`
LEFT JOIN `relation` ON `kop_header`.`relation_id` =`relation`.`id`
WHERE `relation_id` = '$id[$i]'";
$query27 =
"SELECT * FROM `order_line`
LEFT JOIN `relation` ON `order_line`.`relation_id` = `relation`.`id`
WHERE `relation_id` = '$id[$i]'";
$query21 =
"SELECT * FROM `net_price`
LEFT JOIN `relation` ON `net_price`.`relation_id` = `relation`.`id`
WHERE `relation_id` = '$id[$i]'";

i want to delete those table from that code
can i delete all of that 3 table with 1 code?

i havent try this code:
"DELETE * FROM `net_price`
LEFT JOIN `relation` ON `net_price`.`relation_id` = `relation`.`id`
WHERE `relation_id` = '$id[$i]'";
because im afraid i'll delete the table, is this code right? & (same question) how to delete 3 table with 1 code?
thx