在SQL查询Codeigniter中插入PHP变量

Question

I'm using Codeigniter to use some queries and this is my code so far. is my code correct?

$this->db->select("(SELECT SUM(grand_total) FROM Sales_order WHERE member = '2') - (SELECT SUM(amount) FROM payment WHERE member_id = '2')  AS total_sales");

and how to change number 2 with this variable
$this->session->userdata('ID')

Answer 1

Try this

$this->db->select("(SELECT SUM(grand_total) FROM Sales_order WHERE member = '".$this->session->userdata('ID')."') - (SELECT SUM(amount) FROM payment WHERE member_id = '".$this->session->userdata('ID')."')  AS total_sales"');