Question

I’m working with the images table. I need to make sure each player has a primary image if he has more than 1 image. In the following example dataset, this would update either myimage.jpg or hisimage.jpg’s primary to 1 and only1image.jpg’s primary to 1.

Table:  Images

Playerid - 16
Image  - myimage.jpg
primary - 0

Playerid - 16
Image  - hisimage.jpg
primary - 0

Playerid - 17 
Image - only1image.jpg
primary - 0

Playerid - 18 
Image - jamison.jpg
primary - 1

Answer 1

I’m assuming there must be a Player table? If so, you could use the following…

(This is in MS SQL Server syntax, but the logic should hold in MySQL.)

UPDATE
  Images
SET
  Primary = 1
FROM
  Player
INNER JOIN
  Image
    ON Image.ID = (SELECT MIN(lookup.ID) FROM Image AS lookup WHERE lookup.playerID = Player.ID)
WHERE
  NOT EXISTS (SELECT 1 FROM Image AS lookup WHERE lookup.playerID = Player.ID AND lookup.Primary = 1)

This deliberately chooses the image with the lowest ID to set as primary. Alter the correlated sub-query to implement different logic.

EDIT

A version that doesn’t use the Player table, but possibly slower (It would need testing)…

UPDATE
  Image
SET
  Primary = 1
WHERE
  ImageID = (SELECT MIN(lookup.ID) FROM Image AS Lookup WHERE lookup.PlayerID = Image.PlayerID)
  AND NOT EXISTS (SELECT 1 FROM Image AS Lookup WHERE lookup.PlayerID = Image.PlayerID AND lookup.Primary = 1)