You've got two different ways of doing this (I'm going to use the SQL I know, from Oracle, but the concepts the same, if MySQL doesn't support the same syntax):

DELETE FROM source dup
WHERE EXISTS (
  SELECT NULL
  FROM source 
  WHERE dup.field1=source.field1
    AND dup.field2=source.field2
    AND source.key<dup.key)

[download]
which simply delete all records which have a higher key value, but are identical on fields 1 & 2 (extend the list as necessary). How efficient this'll be depends on your database. But all the information is there, so it could be your best bet.

The other option, using perl is along the lines of: 

my $data=$dbh->prepare("SELECT key, field1, field2 FROM source ORDER B
+Y field1, field2");
my $del=$dbh->prepare("DELETE FROM source WHERE key=?");
my @last;
while (my @record=$data->fetchrow_array()) {
  if ($record[1] eq $last[1] &&
      $record[2] eq $last[2]) {
    $del->execute($record[0]);
  }
  @last=@record;
}
$data->finish();
$del->finish();

[download]
Disclaimer: I've just made this up, so I may have got the specifics wrong, but hopefully you get the general idea: keep pulling the records out, in order of the fields you want to match, and when you find a correspondance, kill the duplicate.

--
Tommy
Too stupid to live.
Too stubborn to die.

In reply to Re: Removing duplicates in MySQL by tommyw
in thread Removing duplicates in MySQL by shaolin_gungfu

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