如何确保每个playerid拥有至少1个主图像，如果他有超过0个图像（mysql）

Question

我正在使用图片表。我需要确保每个玩家有一张主图像，如果他有超过1张图像。在下面的示例数据集中，这会将myimage.jpg或hisimage.jpg的primary更新为1，将only1image.jpg的primary更新为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

我假设必须有一张播放器表？如果是这样，您可以使用以下内容......

（这是MS SQL Server语法，但逻辑应该存在于MySQL中。）

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)

这故意选择具有最低ID的图像设置为主要图像。改变相关的子查询以实现不同的逻辑。

修改

不使用Player表的版本，但可能更慢（需要测试）......

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)

Answer 2

这是@Dems的分拆，这对我来说更有意义

UPDATE Images SET `primary` = 1 WHERE Player IN (
    SELECT Player FROM (
        SELECT Player, MAX(`primary`) as max_prim FROM Images GROUP BY Player
    ) as MPrim WHERE max_prim = 0
)

Answer 3

或者，您可以将primary默认设置为1，并按(Player,primary)创建唯一性并添加ON DUPLICATE KEY UPDATE primary=0

Answer 4

考虑重构你的表格。

在播放器表格中有一列指向作为主图像的图像行，如下所示：

player
---------
player_id
primary_image_id


image
---------
image_id
player_id

这样，玩家只能拥有一张适用的主图像。