mysql select default image from other table if not exist

Question

I have a album gallery with data schema like below

| album_id | album_title |
| 1        |  test       |
| 2        |  test123    |
| 3        |  testing    |

| img_id   | img_albumid | img_full_path  | img_album_cover
| 1        |  1          | /blabla/1.jpg  |  0
| 2        |  1          | /blabla/2.jpg  |  1
| 3        |  1          | /blabla/3.jpg  |  0
| 4        |  2          | /blabla/4.jpg  |  0
| 5        |  2          | /blabla/5.jpg  |  1
| 6        |  3          | /blabla/6.jpg  |  0
| 7        |  3          | /blabla/7.jpg  |  0

I can display the album by cross join the image. The issue is, I want to set album cover default image. The cover album will display from image table if user has set it but just get any image from img as cover if the cover album not set. So far this query works, but not for cover album

SELECT album_id, album_title, img_full_path
FROM album 
LEFT JOIN image ON album_id = img_albumid
WHERE img_albumid != 0
GROUP BY(album_id) 
limit 10

How to do it with php and mysql query? Thanks

Answer 1

Use IFNULL() function:

SELECT album_id, album_title, IFNULL(img_full_path, 'default.jpg') as img_full_path
FROM album 
LEFT JOIN image ON album_id = img_albumid
WHERE img_albumid != 0
GROUP BY(album_id) 
limit 10

Source: http://dev.mysql.com/doc/refman/5.0/en/control-flow-functions.html

You might even use subquery, which should contain only one row and column, like this:

SELECT
    album_id,
    album_title,
    IFNULL(img_full_path, (
        SELECT
            img_full_path
        FROM
            image
        WHERE
            (img_albumid = album_id)
            AND
            NOT (img_full_path IS NULL)
        ORDER BY
            RAND()
        LIMIT 1)
    ) as img_full_path
FROM
    album LEFT JOIN image ON album_id = img_albumid
WHERE
    img_albumid != 0
GROUP BY
    album_id
LIMIT 10