To tell you the truth, your code is horrible.

• You're not using placeholders
• You're warning the return value of a print statement. Why?
• You're undefining @data_array, yet @data_array is neither used nor declared in your code.
• What does this code do, anyway? Your description wasn't very clear, and from the looks of your code its use appears to be restricted to a very small scope.

Here's a rewrite:

# "RaiseError => 1" tells DBI to die on errors.
my $dbh = DBI->connect($DSN, $username, $password, { RaiseError => 1 }
+);

my $sth;

$sth = $dbh->prepare("
          SELECT table_name, column_name
          FROM Dba_tab_columns
          WHERE owner = ?
          ORDER BY table_name, column_name
        ");

$sth->execute($schema);

my $table_column = $sth->fetchall_arrayref;

$sth->finish;
        
for my $tcr (@{$table_column}) {
  if ($tcr->[0] eq "EMP") {
    my $sth = $dbh->prepare("SELECT " . $tcr->[1] . " FROM " . $schema
+ . $tcr->[0]);
    $sth->execute;

    my $column_data = $sth->fetchall_arrayref;
    $sth->finish;
                
    # This for-loop create a hash of a hash of an array with the keys 
+{table name} and {column name}
    for my $row (@{$column_data}) {
      push @{ $tables{$tcr->[0]}{$tcr->[1]} }, $row->[0];             
+      
    }
  }
}
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[ ar0n -- want job (boston) ]