difference between $query>num_rows() and $this->db->count_all_results() in CodeIgniter & which one is recommended

In a scenario I n开发者_如何学Goeed to know the count of recordset a query will return, which in codeigniter can be done by $query->num_rows() or $this->db->count_all_results(). Which one is better and what is the difference between these two?

With num_rows() you first perform the query, and then you can check how many rows you got. count_all_results() on the other hand only gives you the number of rows your query would produce, but doesn't give you the actual resultset.

// num rows example
$this->db->select('*');
$this->db->where('whatever');
$query = $this->db->get('table');
$num = $query->num_rows();
// here you can do something with $query

// count all example
$this->db->where('whatever');
$num = $this->db->count_all_results('table');
// here you only have $num, no $query

$this->db->count_all_results is part of an Active Record query (preparing the query, to only return the number, not the actual results).

$query->num_rows() is performed on a resultset object (after returning results from the DB).

We can also use

return $this->db->count_all('table_name');  

or

$this->db->from('table_name');
return $this->db->count_all_result();

or

return $this->db->count_all_result('table_name');

or

$query = $this->db->query('select * from tab');  
return $query->num_rows();

Which one is better and what is the difference between these two Its almost imposibble to me, someone just want to get the number of records without re-touching or perform another query which involved same resource. Furthermore, the memory used by these two function is in same way after all, since with count_all_result you still performing get (in CI AR terms), so i recomend you using the other one (or use count() instead) which gave you reusability benefits.

There are two ways to count total number of records that the query will return. First this

$query = $this->db->query('select blah blah');  
return $query->num_rows();

This will return number of rows the query brought.

Second

return $this->db->count_all_results('select blah blah');

Simply count_all_results will require to run the query again.

Total number of results

$this->db->count_all_results('table name');

Simply as bellow;

$this->db->get('table_name')->num_rows();

This will get number of rows/records. however you can use search parameters as well;

$this->db->select('col1','col2')->where('col'=>'crieterion')->get('table_name')->num_rows();

However, it should be noted that you will see bad bad errors if applying as below;

$this->db->get('table_name')->result()->num_rows();

$sql = "select count(*) as row from login WHERE firstname = '" . $username . "' AND password = '" . $password . "'";
    $query = $this->db->query($sql);
    print_r($query);exit;
    if ($query->num_rows() == 1) {
    return true;
    } else {
    return false;
    }