Question

我有一个带有CASE语句的查询，该语句确定变量object_name此变量是从x_ambitions表或x_trybes表派生的。下面的查询被组合在一起，这样我只需执行一个SQL查询就可以保持简单。

我已将SELECT语句拆分为两个，以便您更好地理解。以下两个查询。工作并从数据库中提取正确的object_name。

我在组合两个查询时遇到的问题是'new_join_ambition','new_created_ambition','new_liked_ambition'个对象在LEFT JOIN中返回NULL。

在合并查询中，如果我将案例'new_join_ambition','new_created_ambition','new_liked_ambition'置于'new_join_trybe','new_created_trybe','new_liked_trybe'个案例之上。相反的情况发生了trybe行返回NULL。

两个SQL查询：

答:(检索对象A）

SELECT 
    s.id, 
    s.object_id, 
    s.type, 
    s.postee_id, 
    s.user_id,
    s.text,
    s.registered,
    CONCAT(u.x_first_name,' ',u.x_last_name) AS postee_name,
    ui.image_id AS postee_image_id,
    CASE s.type
       WHEN 'new_join_ambition' 
            OR 'new_created_ambition' 
            OR 'new_liked_ambition'         
          THEN a.name
          ELSE 'a'
    END AS object_name
FROM 
    x_share s
LEFT JOIN 
    x_user u ON u.id = s.postee_id
LEFT JOIN 
    x_user_images ui ON ui.user_id = s.postee_id
LEFT JOIN 
    x_ambitions a ON s.type IN ('new_join_ambition', 'new_created_ambition', 'new_liked_ambition') AND s.object_id = a.id
LEFT JOIN 
    x_ambition_invites ai ON s.type IN ('new_join_ambition') AND s.object_id = ai.ambition_id AND s.postee_id = ai.to
LEFT JOIN 
    x_ambition_likes al ON s.type IN ('new_liked_ambition') AND s.object_id = al.ambition_id AND s.postee_id = al.profile_id
LEFT JOIN 
    x_ambition_owner aoo ON s.type IN ('new_created_ambition') AND s.object_id = aoo.ambition_id
WHERE 
    s.user_id = '%s'
ORDER BY 
    s.registered DESC

B :(检索对象B）

SELECT 
    s.id, 
    s.object_id, 
    s.type, 
    s.postee_id, 
    s.user_id,
    s.text,
    s.registered,
    CONCAT(u.x_first_name,' ',u.x_last_name) AS postee_name,
    ui.image_id AS postee_image_id,
    CASE s.type
       WHEN 'new_join_trybe'
            OR 'new_created_trybe' 
            OR 'new_liked_trybe'
          THEN t.name
          ELSE 'a'
    END AS object_name
FROM 
    x_share s
LEFT JOIN 
    x_user u ON u.id = s.postee_id
LEFT JOIN 
    x_user_images ui ON ui.user_id = s.postee_id
LEFT JOIN 
    x_trybes t ON s.type IN ('new_join_trybe', 'new_created_trybe', 'new_liked_trybe') AND s.object_id = t.id
LEFT JOIN 
    x_trybe_invites ti ON s.type IN ('new_join_trybe') AND s.object_id = ti.trybe_id AND s.postee_id = ti.to
LEFT JOIN 
    x_trybes_likes tl ON s.type IN ('new_liked_trybe') AND s.object_id = tl.trybe_id AND s.postee_id = tl.profile_id
LEFT JOIN 
    x_trybe_owner too ON s.type IN ('new_created_trybe') AND s.object_id = too.trybe_id
WHERE 
    s.user_id = '%s'
ORDER BY 
    s.registered DESC

我已经运行了两个查询并捕获了两个查询结果的图像。

设置A：

设置B：

如何在没有object_name返回NULL的情况下组合这两个？如果您有任何疑问，请使用评论，我会毫不犹豫地回复。

提前致谢

Answer 1

我不知道您的查询的其余部分，但您的case声明不正确。你有：

(CASE s.type
          WHEN 'new_join_ambition' OR 'new_created_ambition' OR 'new_liked_ambition'
          THEN a.name
          ELSE 'a'
END) AS object_name

OR最终将值视为数字，因此相当于WHEN 0 THEN . . .。

你想要的是这种形式的case：

(CASE WHEN s.type IN ('new_join_ambition', 'new_created_ambition', 'new_liked_ambition')
      THEN a.name
      ELSE 'a'
 END) AS object_name

MySQL CASE LEFT JOINS返回NULL

1 个答案: