Question

我有两个类似的SQL查询来解决问题，但只有第二个可以解决问题。

问题是：

仅考虑肌肉疾病，写下一个查询，删除至少有两种（肌肉）疾病患者的起病，最终恢复。

数据库具有以下结构：

Onset (Patient,Pathology,OnsetDate,RecoveryDate)
Pathology (Name,BodyPart)

这是我的第一个代码：

DELETE ES.* 
FROM Onset ES NATURAL JOIN
(
SELECT E.Patient, E.Pathology, E.OnsetDate
FROM Onset E INNER JOIN Pathology P ON E.Pathology=P.Name
WHERE P.BodyPart='Muscles'
      AND E.RecoveryDate IS NOT NULL
      AND 2<=(SELECT COUNT(DISTINCT E2.Pathology)
              FROM Onset E2 INNER JOIN Pathology P2 ON E2.Pathology=P2.Name
              WHERE P2.BodyPart='Muscles'
                    AND E2.Patient=E.Patient
                    AND E2.RecoveryDate IS NOT NULL
             )
) AS D;

这是我的第二个代码：

DELETE E.* FROM Onset E 
INNER JOIN Pathology PA ON E.Pathology = PA.Name
NATURAL JOIN(
    SELECT E2.Patient
    FROM Onset E2 INNER JOIN Pathology P ON E2.Pathology = P.Name
    WHERE E2.RecoveryDate IS NOT NULL
        AND P.BodyPart = 'Muscles'
    GROUP BY E2.Patient
    HAVING COUNT(DISTINCT E2.Pathology) >= 2
) AS D
WHERE PA.BodyPart = 'Muscles'
   AND E.RecoveryDate IS NOT NULL;

第二个代码工作正常，而第一个代码则返回常见错误：

错误代码：1093。您无法在更新中指定目标表'ES' FROM子句

我知道当您尝试从子查询中使用的表中删除时会发生这种情况，并且您可以使用派生表来绕过它。虽然，我的代码都在子查询中使用Onset，并且都使用派生表。那么，为什么第一个不起作用，而第二个呢？

提前致谢！

Answer 1

在delete子句中删除from子句

 DELETE ES  
 NATURAL JOIN
 (
 SELECT E.Patient, E.Pathology, E.OnsetDate
 FROM Onset E INNER JOIN Pathology P ON E.Pathology=P.Name
 WHERE P.BodyPart='Muscles'
      AND E.RecoveryDate IS NOT NULL
      AND 2<=(SELECT COUNT(DISTINCT E2.Pathology)
              FROM Onset E2 INNER JOIN Pathology P2 ON E2.Pathology=P2.Name
              WHERE P2.BodyPart='Muscles'
                    AND E2.Patient=E.Patient
                    AND E2.RecoveryDate IS NOT NULL
             )
 ) AS D;

确保你有一个合适的（在哪里）条件;

MySQL删除：两个相似的代码，只有一个有效

1 个答案: