这个活动记录查询有什么作用？

I am working on a existing project whose code is written by earlier developer. When I read a function in the model it was written:

        $this->db->select('1', FALSE);
    $this->db->where('product_id', $product_id);
    $query = $this->db->get('product');     
    if ($query->num_rows() == 1) {
        return false;
    }
        return true;

I am wondering what does this first statement does? i.e $this->db->select('1', FALSE); because there is no column named 1 in the product table. I searched online but there is no help. Would any explain?

As I haven't seen anything like that so far, I would do a

 echo $this->db->last_query()

after the $this->db->get() just to see the actual sql query for that.

SELECT 1 FROM

It is used to determine the existence of a result. It will return a column of 1's for every row in the result.

SELECT 1;

=> 1

SELECT 1 + 1;

=> 2

Codeigniter you can use this query when

$this->db->select('1', FALSE);

If you don't turn it to FALSE, you can only select columns

$this->db->select('column', TRUE);