Illuminate\Database\Connection::raw PHP Method

    public function raw($value)
    {
        return new Expression($value);
    }

 /**
  * Perform column search.
  */
 public function doColumnSearch()
 {
     $columns = $this->input['columns'];
     for ($i = 0, $c = count($columns); $i < $c; $i++) {
         if ($this->isColumnSearchable($columns, $i)) {
             $column = $columns[$i]['name'];
             $keyword = $this->setupKeyword($columns[$i]['search']['value']);
             if (isset($this->filter_columns[$column])) {
                 $method = $this->filter_columns[$column]['method'];
                 $parameters = $this->filter_columns[$column]['parameters'];
                 $this->compileFilterColumn($method, $parameters, $column);
             } else {
                 $column = $this->wrapValue($column);
                 if ($this->isCaseInsensitive()) {
                     $this->query->whereRaw('LOWER(' . $column . ') LIKE ?', [Str::lower($keyword)]);
                 } else {
                     $col = strstr($column, '(') ? $this->connection->raw($column) : $column;
                     $this->query->whereRaw($col . ' LIKE ?', [$keyword]);
                 }
             }
         }
     }
 }