IF, Join and concat not working in codeigniter - sql

Question

I have two tables, one of which contains 3000 area codes (so just the first half of the postcode) and the other table containing shops details with a column called postcodes_covered which are all the area codes that a particular shop covers for example:
shop 1 (AB1,AB2,AB3,AB4,AB5...), shop 2 (E15,E13,E14 ...) etc. I need to create a report which contains the 3000 area codes and a column that says "Yes" if an area code from table 2 is contained in table 1 or "No" if that area code is not covered. I have written an SQL query which works fine however, i need to write it in codeigniter. The code i have written for codeigniter doesn't seem to work and i don't know why?
SQL query:
select bodyshops_postcode_allocation.area_code,if(postcodes_covered is null,"No","Yes") as "YeN" from bodyshops_postcode_allocation left join bodyshops on bodyshops.postcodes_covered like concat("%",bodyshops_postcode_allocation.area_code,"%");
Codeigniter:
function postcode_allocation()
{
$this->db->select('bodyshops_postcode_allocation.area_code as area_code')
->select('IF(bodyshops.postcodes_covered is null, "No", "Yes") as match_found')
->join('bodyshops', 'bodyshops.postcodes_covered LIKE CONCAT("%",bodyshops_postcode_allocation.area_code,"%")')
->from('bodyshops_postcode_allocation');
$this->load->dbutil();
$data = $this->dbutil->csv_from_result($this->db->get(''));
$this->output->set_header("Content-type: application/vnd.ms-excel");
$this->output->set_header("Content-disposition: attachment; filename=postcode_allocation.csv; size=".strlen($data));
$this->output->set_output($data);
}

Answer 1

When using SQL function like this in CodeIgniter, you need to tell it not to try to escape the query.
->select('IF(bodyshops.postcodes_covered is null, "No", "Yes") as match_found', FALSE)
The FALSE tells CodeIgniter to leave the string as-as and not try to add backticks to it. It doesn't know how to add them in this case, so it messes up your query.
P.S. your join needs to be:
->join('bodyshops', 'bodyshops.postcodes_covered LIKE CONCAT("%",bodyshops_postcode_allocation.area_code,"%")', 'left')
If you want a LEFT JOIN, you need to tell it so.
P.P.S. $this->db->get('') should really just be $this->db->get(). Don't pass it a blank string.