[Resolved] compare tables and delete dups

[cbrknight]

This is probably easy but when I searched I only found solutions to finding dupes in one table while inserting.

I have two tables. I need to compare one field in both tables. If the record exists in table 2 I must delete it from table 1

I tried to just select the duplicate records with

$sql = "SELECT mainfile.test.telephone FROM mainfile_test WHERE mainfile_test.telephone=mainfile.telephone";

I also tried the delete like so...
$sql = "DELETE FROM mainfile_test WHERE mainfile_test.telephone=mainfile.telephone";

What am I doing wrong?

[devinemke]

assumptions:
1. you are using mySQL
2. the primary key field in the mainfile_test table is called "id"

$result = mysql_query('SELECT mainfile_test.id FROM mainfile_test, mainfile WHERE mainfile_test.telephone = mainfile.telephone') or exit(mysql_error());
while ($row = mysql_fetch_assoc($result)) {$delete[] = $row['id'];}
$result = mysql_query('DELETE FROM mainfile_test WHERE id IN(' . implode(',', $delete) . ')') or exit(mysql_error());
echo mysql_affected_rows() . ' deleted from mainfile_test';