MySQL CASE 查询与 INNER JOIN

Question

我有 1 个字符串类型的表。（photo_add、photo_comment 等）然后我有 4 个与这些类型连接的其他表。

我需要进行一个查询，根据类型从所有这些表中选择数据。

我创建了这个，但它不起作用。

SELECT DISTINCT a.id, a.event, a.params, a.created_at, a.item_id, a.sender_id, a.receiver_id, u.name, u.id as userid 
FROM `eva49_lovefactory_activity` a, eva49_users u 
CASE a.event 
  WHEN "photo_add" THEN 
    INNER JOIN eva49_lovefactory_photos lp ON lp.id = a.item_id AND lp.fsk18 = -1
  WHEN "group_create" THEN 
     INNER JOIN eva49_lovefactory_groups lg ON lg.id = a.item_id AND lg.fsk18 = -1 
  WHEN "photo_comment" THEN 
     INNER JOIN eva49_lovefactory_item_comments lic ON lic.item_id = a.item_id AND lic.fsk18 = -1 
  WHEN "profile_comment" THEN 
     INNER JOIN eva49_lovefactory_item_comments lic ON lic.item_id = a.item_id AND lic.fsk18 = -1 
  WHEN "profile_comment" THEN 
    INNER JOIN eva49_lovefactory_profiles lp ON lp.user_id = a.receiver_id AND lp.status_fsk18 = -1 
  ELSE 1=1 
END 
WHERE (u.id = a.sender_id OR u.id = a.receiver_id) and (u.id <> 379) 
ORDER BY a.created_at DESC LIMIT 0, 10

有什么办法可以配对桌子吗？数据库结构是这样给我的。

编辑：

有一个表“eva49_lovefactory_activity”包含有关最近活动的信息。它有一个“事件”列，其中包含带有事件名称的字符串（photo_add、photo_comment 等）

还有其他表 - eva49_lovefactory_photos、eva49_lovefactory_profiles、eva49_lovefactory_groups 等。在这些表中，我必须查找该项目是否已获得管理员批准。如果是的话我可以展示一下。(fsk18 = -1)

Answer 1

将 CASE 条件移至 JOIN 条件并执行 LEFT JOIN..

SELECT DISTINCT a.id, a.event, a.params, a.created_at, a.item_id, a.sender_id, a.receiver_id, u.name, u.id as userid 
FROM `eva49_lovefactory_activity` a, eva49_users u 

    LEFT JOIN eva49_lovefactory_photos lp ON lp.id = a.item_id AND lp.fsk18 = -1
               AND a.event='photo_add'
    LEFT JOIN eva49_lovefactory_groups lg ON lg.id = a.item_id AND lg.fsk18 = -1 
               AND a.event='group_create'
    LEFT JOIN eva49_lovefactory_item_comments lic ON lic.item_id = a.item_id AND 
              lic.fsk18 = -1     AND a.event='photo_comment'
    LEFT JOIN eva49_lovefactory_item_comments lic ON lic.item_id = a.item_id AND 
              lic.fsk18 = -1     AND   a.event='profile_comment'

WHERE (u.id = a.sender_id OR u.id = a.receiver_id) and (u.id <> 379) 
ORDER BY a.created_at DESC LIMIT 0, 10