SQL Injection: How to save from it in OpenCart

Tips:

 Always use $this->db->escape() after reading it from $this->request or $_GET

what is sql injection:

below query can be hacked:

[select * from my_table where var='$var']

if i pass $var=' OR delete from my_table where 1

It will delete all content of my_table.

$this->db->escape ...escape ' field so save from injection.