MySQL and using only some results - mysql

Question

I am trying to create a directory and having an issue calling the "listing image" in the results. The issue is that only some listings will have images, otherwise if they do not, I want them to use the default-image I have set up. When I try and add in the 'image' table to my query, it returns ONLY the results that have an image available (leaving out the other listings that do not have an image).
Here is my code:
public function search($neighborhood = null, $biz_filter = null) {
$neighborhood = $this->uri->segment(3);
$biz_filter = $this->uri->segment(4);
// SELECT
$this->db->select('*');
// MAIN TABLE TO GRAB DATA
$this->db->from('biz');
// TABLES TO JOIN
$this->db->join('city', 'city.city_id = biz.biz_cityID');
$this->db->join('zip', 'zip.zip_id = biz.biz_zipID', 'zip.zip_cityID = city.city_id');
$this->db->join('state', 'state.state_id = city.city_stateID');
$this->db->join('neighborhood', 'neighborhood.neighborhood_id = biz.biz_neighborhoodID');
$this->db->join('biz_filter', 'biz_filter.bizfilter_bizID = biz.biz_id');
$this->db->join('biz_category', 'biz_category.bizcategory_id = biz_filter.bizfilter_bizcategoryID');
if ($neighborhood != "-" AND $biz_filter != "-") {
$this->db->where('biz_category.bizcategory_slug', $biz_filter);
$this->db->where('neighborhood.neighborhood_slug', $neighborhood);
} elseif ($neighborhood != "-" AND $biz_filter == "-") {
$this->db->where('neighborhood.neighborhood_slug', $neighborhood);
} elseif ($neighborhood == "-" AND $biz_filter != "-") {
$this->db->where('biz_category.bizcategory_slug', $biz_filter);
} else {
}
// ORDER OF THE RESULTS
$this->db->group_by('biz_name asc');
// RUN QUERY
$query = $this->db->get();
// IF MORE THAN 0 ROWS ELSE DISPLAY 404 ERROR PAGE
return $query;
}
How can I add in the separate table, 'image' that holds the logo images ('image.image_file'). The 'image' table and 'biz' table are connected through the business ID i pass through each table (image.biz_id = biz.biz_id).
Anyone know how to resolve the query to work properly?

Answer 1

Just use
$this->db->join('image', 'image.biz_id = biz.biz_id', 'left');
To LEFT JOIN your image table. When there is no records in the table for the biz_id the image.image_file will have null values. Read here for more information.
You can use a COALESCE function to replace the "null" images with a predefined default value. Just replace your line with $this->db->select('*'); to this one:
// SELECT
$this->db->select("*, COALESCE(image.image_file, 'images/not_found.png') as my_image_file");
When you render the output make sure you use my_image_file column for the image.
On a side note: avoid using '*' in the select. Select only those columns you actually need. Selecting all columns unnecessarily increases the load on the database server resources.