'Greater than or equal' and 'less than or equal' CODEIGNITER

from what i know, you can write them like this

$this->db->select('COUNT(payment.keyid) AS rec_count, product_key.client_name, product_key.contact_email, product_key.status, product_key.id, payment.paymentdate, (payment.id) as pid, payment.subscription_type', false);
$this->db->where('payment.paymentdate >= "2013-08-01"');
$this->db->where('payment.paymentdate <= "2013-08-31"');
$this->db->where('status', 'purchased');
$this->db->group_by('product_key.id');
$this->db->order_by('client_name', 'asc');
$this->db->join('payment', 'payment.keyid=product_key.id', 'LEFT OUTER')
$this->db->get('product_key');

Try to change the =< to <= like

->where('payment.paymentdate >=', $month_start)
->where('payment.paymentdate <=', $month_end)

And better but not cumpolsury to join the table before the where condition.Now your query should be like

->select('COUNT(payment.keyid) AS rec_count')
->select('product_key.client_name, product_key.contact_email, product_key.status, product_key.id, payment.paymentdate, (payment.id) as pid,payment.subscription_type')
->from('product_key')         
->join('payment', 'payment.keyid=product_key.id', 'left outer')    
->where('payment.paymentdate >=', $month_start)
->where('payment.paymentdate <=', $month_end)
->where('status', 'purchased')
->order_by('client_name', "asc")
->group_by('product_key.id')
->get()

Change =< to <=.

I also tested your current query in phpmyadmin, because i could not believe that it does not throw an error. But mine does it. So your query should not work in phpmyadmin.

#1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '=< ...' at line ...