public function select_many_expr()
{
$columns = func_get_args();
if (!empty($columns)) {
$columns = $this->_normalise_select_many_columns($columns);
foreach ($columns as $alias => $column) {
if (is_numeric($alias)) {
$alias = null;
}
$this->select_expr($column, $alias);
}
}
return $this;
}