Question

我有一个查询，查找符合给定条件的学生记录（相同的ClassNum和匹配的名称或匹配的电子邮件）。任何状态为“已删除”的学生都应该被忽略。

以下查询找到正确的重复项并忽略“学生”中已删除的学生，但我找不到一种方法来阻止它与'dup'中的已删除学生匹配。

案例1：有两个“John Smith”在同一个班级注册。该查询将返回2行，每个John Smith找到一行。这是正确的行为。

案例2：有两个“John Smith”在同一个班级注册，但其中一个的状态为“已删除”。该查询返回未删除的John Smith的一行。这不是我想要的。

我尝试将两个WHERE子句放在ON部分中，将ON和WHERE之间的子句分开等，但都给出了相同的结果。

    SELECT DISTINCT Students.Id,
                    Students.ClassNum,
                    Students.Lastname,
                    Students.Firstname,
                    Students.Status,
                    Students.Email
               FROM Students
         INNER JOIN (
                      SELECT Id,ClassNum,Email,Lastname,Firstname,Status 
                        FROM Students
                    ) dup
                 ON (    Students.Id != dup.Id 
                     AND Students.ClassNum = dup.ClassNum 
                     AND (   (    Students.Email = dup.Email 
                              AND Students.Email != ''
                             )
                          OR (    Students.Lastname = dup.Lastname 
                              AND Students.Firstname = dup.Firstname)
                         )
                     )
               WHERE Students.Status != 'Deleted' 
                 AND dup.Status != 'Deleted'

Answer 1

逻辑 OR 通常表示SQL UNION;所以试试这个：

SELECT Students.Id,
       Students.ClassNum,
       Students.Lastname,
       Students.Firstname,
       Students.Status,
       Students.Email
  FROM Students lhs
  JOIN Students rhs
     on lhs.ClassNum  = rhs.ClassNum
    and lhs.Firstname = rhs.Firstname
    and lhs.LastName  = rhs.LastName
    and lhs.Status   != 'DELETED'
    and rhs.Status   != 'DELETED'
UNION
SELECT Students.Id,
       Students.ClassNum,
       Students.Lastname,
       Students.Firstname,
       Students.Status,
       Students.Email
  FROM Students lhs
  JOIN Students rhs
     on lhs.ClassNum  = rhs.ClassNum
    and lhs.Email     = rhs.Email
    and lhs.Status   != 'DELETED'
    and rhs.Status   != 'DELETED'

使用Join＆amp; amp;查找重复项哪里

1 个答案: