SELECT @columns, COUNT(*)
FROM $table
GROUP BY @columns
HAVING COUNT(*) > 1

##</code><code>##

@key_cols1 = qw(account_id group_id);
@key_cols2 = qw(account_id manager_id asset_id);
# Later...
$set1_sql = 'SELECT ' . join(',', @key_cols1)
   . 'FROM ' . $table1_name
   . 'WHERE ' . $table1_cond
# You get the idea