If the tables are too big for that, then you'll need to do a bit more work. For each pair of tables, get a list of the values of the primary key(s), and find any differences - that'll catch added and deleted records. Then you'll also need to compare the individual records for each value of the primary key that is common to both tables

For instance, supposing the primary key my_key is of some string type:

my $sql = <<EOSQL;
  select my_key, foo1, foo2, ...
    from bar
    order by my_key
EOSQL

my $sth1 = $dbh1->prepare($sql);
my $sth2 = $dbh2->prepare($sql);

unless ($sth1->execute and $sth2->execute) {
  die ...;
}
my $row1 = $sth1->fetchrow_arrayref;
my $row2 = $sth1->fetchrow_arrayref;

while ($row1 and $row2) {
  if ($row1->[0] lt $row2->[0]) {
    print "$row1->[0] only in db 1\n"
    $row1 = $sth1->fetchrow_arrayref;
  }
  elsif ($row1->[0] gt $row2->[0]) {
    print "$row2->[0] only in db 2\n"
    $row2 = $sth2->fetchrow_arrayref;
  }
  else {
    # a better equality check for rows could be needed
    # if the db software is different or if the db
    # schemas are not identical:
    if ("@$row1" eq "@$row2") {
      print "row $row1->[0] differ\n"
    }
    $row1 = $sth1->fetchrow_arrayref;
    $row2 = $sth2->fetchrow_arrayref;
  }
}
while ($row1) {
  print "$row1->[0] only in db 1\n"
  $row1 = $sth1->fetchrow_arrayref;
}
while ($row2) {
  print "$row2->[0] only in db 2\n"
  $row2 = $sth2->fetchrow_arrayref;
}
[download]

I researched this the other day, looking for a tool to help upgrading schemas, and my impression is that the capabilities seems a bit spotty, and the database support is somewhat uneven. If you use MySQL it may work just fine, if you use Oracle (like I do in the current project) or some other database, it may depend on what features you use in the schema. For example, the Oracle diff seemed to lack support for sequences and partitions, just to name a few things.

(One other tool I looked at briefly is Embarcadero Change Manager, which looked very competent and feature-complete. It operates on db connections though, not SQL DDL statements which I would prefer.)

/J

Your question isn't very clear. Are you trying to find out the difference between the structure or content of the two databases?

It might be helpful to review How (Not) To Ask A Question

--roboticus