how to use DISTINCT here in my query CODEIGNITER - php

Question

$q = $this->db->select('
books.title,
reserved_books.id,
reserved_books.isbn,
reserved_books.price,
reserved_books.item_sold,
reserved_books.date_sold,
reserved_books.total_amount
')
->from('reserved_books')
->join('books','reserved_books.isbn= books.isbn')
->limit($limit,$offset);
how can i use distinct here in my query?
reserved_books.isbn is the unique one.

Answer 1

Try Below:
$this->db->distinct();
but Distinct will not always work. You should add ->group_by("name_of_the_column_which_needs_to_be unique");
$this->db->group_by('column_name');

Answer 2

You don't need any join
$query=$this->db->distinct()->select('table_attribute')->where('condition')->get('table_name');
return $query->result();

Answer 3

Adds the "DISTINCT" keyword to a query before Select
$this->db->distinct();
Refrence

Answer 4

Here is a way to do this
$select = array(
'books.title',
'reserved_books.id',
'DISTINCT reserved_books.isbn',
'reserved_books.price',
'reserved_books.item_sold',
'reserved_books.date_sold',
'reserved_books.total_amount'
);
$q = $this->db
->select($select)
->from('reserved_books')
->join('books','reserved_books.isbn= books.isbn')
->group_by('reserved_books.isbn')
->limit($limit,$offset);

Answer 5

Here is best way to remove duplicate entry.
$query = $this->db->select("inf.id, inf.sku, inf.fab_id, inf.sku, inf.amount, inf.min_length, inf.num_of_pieces, inf.width ,inf.type")
->join("retailcat","retailcat.sku=SUBSTRING(inf.sku,1,19) AND retailcat.category=218","INNER")
->distinct()
->get("input_factor inf");