Conditional Join: don't join on null - mysql

Question

I have relationships that might not necessarily exist (they could be optional i.e. null); for example, a image may not have an address so it may be null.
I am unsure how to not return all null values.
Is there some condition I can put in place on the join that says if the address is null don't do a join and don't return all the null columns?
SELECT im.title, im.alias_title, im.description, im.main_image, im.hits,
im.show_comment, im.created_on, im.date_taken, im.account_type_id,
c.make, c.model, ad.address_line_1, ad.address_line_2,
spc.state_province_county, tvc.town_village_city, co.country,
ge.latitude, ge.longitude, ge.zoom, ge.yaw, ge.pitch,
us.first_name, us.surname, us.user_set_online, ut.username,
ut.account_type_id, aty.`type`, ufy.realname, ufy.location,
ufy.location, ufy.account_type_id
FROM image im
INNER JOIN user us
ON im.user_id = us.id
LEFT JOIN user_type ut
ON us.id = ut.user_id
LEFT JOIN user_flickr_youtube ufy
ON ut.id = ufy.user_type_id
LEFT JOIN account_type aty
ON ut.account_type_id =aty.id
LEFT JOIN address ad
ON im.address_id = ad.id
LEFT JOIN state_province_county spc
ON ad.state_province_county_id = spc.id
LEFT JOIN town_village_city tvc
ON ad.town_village_city_id =tvc.id
LEFT JOIN country co
ON ad.country_id =co.id
LEFT JOIN geolocation ge
ON im.geolocation_id = ge.id
LEFT JOIN camera c
ON im.camera_id = c.id
WHERE im.alias_title = 'test'
AND im.approved = 'Yes'
AND im.visible = '1'
LIMIT 1;

Answer 1

Is there some condition i can put in place on the join that says if the address is null dont do a join and dont bring me back all the null columns
Yes; you can run a JOIN instead of a LEFT JOIN. But that won't simply exclude the address if it is NULL, it will ignore the whole row altogether.
Usually this kind of situation is either handled by supplying a default value, possibly empty, for example directly in MySQL
SELECT
...COALESCE(ad.address_line_1,'(no address)') AS address_line_1,
COALESCE(ad.address_line_2,'') AS address_line_2, ...
or it is handled by the application:
if row['address_line_1']:
result = result + ("<td class=\"address\">%s</td>" % ( row['address_line_1'] ))
...
This also because a query could potentially return not one record, but several, and of these, some might have a NULL colum and some might not.
UPDATE
There is a way, but it's likely to make milk go sour in cows fifty miles downrange.
This is a proof of concept, on a MUCH smaller query and table, and takes advantage of the possibility of dynamically building a query.
First of all we have our query WHERE condition, here represented by "id = 1". We want to have the name column if the name column is not NULL.
SELECT #address := COALESCE(MIN(',name'),'') FROM client WHERE name IS NOT NULL AND id = 1;
This will return an empty string if the selected column is NULL. Otherwise it will return a comma and the name of that column.
This is the statement that in your case will be humongous, given your query. It contains the same WHERE as before, without the request that the name be NULL. And the field list is now dynamic.
SELECT #string := CONCAT('SELECT id', #address, ' FROM client WHERE id = 1');
Except that #string is, well, a string. To execute it as a query we do
PREPARE query FROM #string;
EXECUTE query;
DEALLOCATE PREPARE query;
How this might interact with your application, I do not dare fathom. I have tried an implementation in PHP on an expendable VM :-), cycling between the values of 1 and 3 (one row has a NULL name, one hasn't).
<?php
// Connect to this VM's local DB
mysql_connect('localhost','root','') or die("Cannot connect");
mysql_select_db('test');
foreach(array(1, 3) as $id)
{
mysql_query("SELECT #address := COALESCE(MIN(',name'),'') FROM client WHERE name IS NOT NULL AND id = $id;");
mysql_query("SELECT #string := CONCAT('SELECT id', #address, ' FROM client WHERE id = ', $id);");
mysql_query("PREPARE query FROM #string;");
$exec = mysql_query("EXECUTE query;");
while($tuple = mysql_fetch_assoc($exec))
{
print implode(" | ", $tuple) . "\n";
}
mysql_query("DEALLOCATE PREPARE query;");
}
?>
The answer seems to indicate it's working:
1 | Rossi
3
(I wouldn't have been surprised if it returned something like 'Ia! Cthulhu fhtagn!').