How can I build multiple queries at once with CodeIgniter QueryBuilder? - codeigniter

Question

I have a complex SELECT with several time consuming calculated fields. I only want the first 100 rows, however, I also need the total rows found. This means executing the query once with LIMIT and once without.
I would like to be able to build two SELECT's simultaneously with CodeIgniter's QueryBuilder and eliminate the time consuming calculated fields on the second query.
I would like to know if there is a good way to do this with QB or should I just build the SELECT without QB.
UPDATE: Apparently I have confused people. I need to do something like this:
To get the records to display:
SELECT id, [ several really time intensive calculated fields ]
FROM table
WHERE [some complicated criteria]
LIMIT 100;
To get the total records I would like to re-use the built query or build a 2nd one simultaneously but without the limit and with only the id field:
SELECT id
FROM table
WHERE [some complicated criteria];
Another option; I have learned that if I put the time intensive calculated fields in a sub SELECT, Postgres will not execute it until the row is actually retrieved.
For now I am manually building two queries but I'd like to do it the correct QueryBuilder way.

Answer 1

There is no way to run multiple query in one statement in codeigniter. But you may do as following
$query1 = $this->db->query('SELECT * FROM table_name LIMIT 10');
$query2 = $this->db->query('SELECT * FROM table_name');
But what I do is make a method and call based on parameter like
public function get_rows($table, $num_rows = FALSE){
$this->db->select('*');
$this->db->from($table);
if($num_rows === FALSE){
$this->db->limit(10);
}
$query = $this->db->get();
if($num_rows){
return $query->num_rows();
}
return $query->result_array();
}
Now you may call it as your requirements
//call for only count rows (without limit)
$this->model_name->get_rows('table_name', TRUE);
//call with limit for result rows
$this->model_name->get_rows('table_name');

Answer 2

with count you can do this with query builder I think
look at this code, you may want something like that
if($limit != null){
$this->db->limit($limit, $offset);
}
if($order_by != null){
$this->db->order_by($order_by, $sort);
}
$query = $this->db->get('courses');
$courses['rows'] = $query->result();
$courses['num_rows'] = $this->db->count_all('courses');
return $courses;