Question

Im trying to do a LEFT JOIN/INNER JOIN/JOIN (forgot the differences, my MySQL knowledge got dusty…) on two tables. one is categories and the other is images .

I want to return a list of all categories with a certain parent value, and for each of these categories return the latest image from images for that category.

I ended up with this query:

SELECT * FROM `categories` AS `a`
         JOIN (SELECT `im`.`preview` AS `preview`,
                      `im`.`cid` AS `cid` 
               FROM `images` AS `im`
               ORDER BY `im`.`cid` DESC) AS `b`
               ON (`a`.`cid` = `b`.`cid`)
         GROUP BY `preview`

This returns a single image from the images table for each row in the category table,
But if I’d try to condition/sort the resulting table, I’ll start getting weird results,
for example changing the end to this or any similar variation:

WHERE `a`.`parent` = 10
GROUP BY `preview`
ORDER BY `a`.`cid

Would appreciate any ideas you would have on this. Thanks in advanced.

Answer 1

You can do it also without join, just using subselect:

SELECT
c.*,
(SELECT preview 
 FROM images img 
 WHERE img.cid = c.cid 
 ORDER BY img.id DESC
 LIMIT 1) AS preview
FROM categories c