my $sort_by = ($sort eq 'date') ? 'date_of' : 'user_name';

my $stmt = 'SELECT * FROM time_sheet WHERE user_id = ? ORDER BY '.$sort_by; 
my $user_time = $dbh->selectall_arrayref($stmt, {Slice => {}}, $user_id);

##</code><code>##

my $stmt;
if ($sort eq 'date') {
   $stmt = 'SELECT * FROM time_sheet WHERE user_id = ? ORDER BY date_of'; 
} else {
   $stmt = 'SELECT * FROM time_sheet WHERE user_id = ? ORDER BY user_name';
}

my $user_time = $dbh->selectall_arrayref($stmt, {Slice => {}}, $user_id);