Mysql 如何将SELECT CASE与子查询一起使用

我的SELECT查询有问题。我尝试检索标记值名称“CallsBy”，但仅当该值为“入口点”时，否则我希望通过另一个子查询计算调用

我有三张桌子：

t_object：包含所有类

t_操作：在所有操作中，链接到t_object.object_ID=t_operation.object_ID

t_operationtag：使用每个操作的所有标记值，链接到t_operation.OperationID=t_operationtag.ElementID

以下是我的表格演示：

第1类的结果是：

Name Operation   | CallsBy
-----------------+------------------------------------
class1Operation1 | class2Operation2, class3Operation1
class1Operation2 | class2Operation3
class1Operation3 | class2Operation3

Name Operation   | CallsBy
-----------------+----------------------------------------------------
class2Operation1 | class1Operation1, class3Operation1,class3Operation3
class2Operation2 | Entry point of Tabidi
class2Operation3 | class1Operation1

Name Operation   | CallsBy
-----------------+---------------------------------------
class3Operation1 | class1Operation2, class3Operation1
class3Operation2 | Entry point of Tabada
class3Operation3 | class2Operation1

第2类的结果是：

Name Operation   | CallsBy
-----------------+------------------------------------
class1Operation1 | class2Operation2, class3Operation1
class1Operation2 | class2Operation3
class1Operation3 | class2Operation3

Name Operation   | CallsBy
-----------------+----------------------------------------------------
class2Operation1 | class1Operation1, class3Operation1,class3Operation3
class2Operation2 | Entry point of Tabidi
class2Operation3 | class1Operation1

Name Operation   | CallsBy
-----------------+---------------------------------------
class3Operation1 | class1Operation2, class3Operation1
class3Operation2 | Entry point of Tabada
class3Operation3 | class2Operation1

第3类的结果是：

Name Operation   | CallsBy
-----------------+------------------------------------
class1Operation1 | class2Operation2, class3Operation1
class1Operation2 | class2Operation3
class1Operation3 | class2Operation3

Name Operation   | CallsBy
-----------------+----------------------------------------------------
class2Operation1 | class1Operation1, class3Operation1,class3Operation3
class2Operation2 | Entry point of Tabidi
class2Operation3 | class1Operation1

Name Operation   | CallsBy
-----------------+---------------------------------------
class3Operation1 | class1Operation2, class3Operation1
class3Operation2 | Entry point of Tabada
class3Operation3 | class2Operation1

以下是用于计算CallsBy（如果不是“入口点”）的子查询：

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我试图编写查询，但没有得到任何结果…

首先让我说，我认为您的数据库表结构和关系可能不是最优的，仅3个表就显得复杂

此外，我相信您在本文中列出的数据与您在db fiddle示例中列出的数据之间存在差异。我创建了所有的表，并用您提供的数据填充它们，我提出的查询结果与您上面列出的预期结果不完全匹配

但是,，我相信这个查询会满足您的需要：如果相应的

t\u operationtag.Property='CallsBy'

和

t\u operationtag.VALUE

包含

Entry point

，那么它将返回

t\u operationtag.VALUE

，否则它将包含

t\u操作。给定对象id的Name

值：

SELECT top.Name,
    CASE WHEN topt2.VALUE IS NOT NULL THEN topt2.Value
    ELSE GROUP_CONCAT(topt1.VALUE)
    END AS CallsBy
FROM t_operation AS top
JOIN t_operationtag AS topt1 ON topt1.ElementID = top.OperationID   
LEFT JOIN t_operationtag AS topt2 ON topt2.ElementID = top.OperationID
    AND topt2.Property = 'CallsBy'
    AND topt2.VALUE LIKE '%Entry point%'
JOIN t_object AS obj ON obj.Object_ID = top.Object_ID
WHERE obj.Object_ID = 1 -- or 2 or 3
GROUP BY top.Name, topt1.PropertyID, topt2.PropertyID
ORDER BY top.Name

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我希望这会有所帮助。

示例数据、所需结果和逻辑解释都会有所帮助。尝试使用外部应用程序而不是嵌套的Select：在我看来这似乎很困难，但我会尝试：）感觉示例不必要地复杂