sql - 如何从此表中检索 DISTINCT 值？

Question

这是我的表值。( 7 条记录 )

SELECT * FROM tbl1

由于我的代表很低，我无法发布图像。所以我在这里链接它 http://i.stack.imgur.com/CFl0u.png

我写了一个查询以避免最后一条记录，但我仍然得到最后一条记录。（我只需要不同的电子邮件）

SELECT DISTINCT CandEmail,CandName,EmployerId,ContNum,IsDeleted,CandPortalId FROM tbl1
WHERE EmployerId = 7 AND IsDeleted = 0

上面的查询仍然检索到与最后一个重复电子邮件记录相同的 7 条记录。

Answer 1

您可以使用ROW_NUMBERwithOVER子句：

WITH CTE AS
(
  SELECT CandEmail,CandName,EmployerId,ContNum,IsDeleted,CandPortalId
        , RN = ROW_NUMBER() OVER (PARTITION BY CandEmail ORDER BY ContNum DESC)
  FROM tbl1
  WHERE IsDeleted = 0
)
SELECT CandEmail,CandName,EmployerId,ContNum,IsDeleted,CandPortalId
FROM CTE WHERE RN = 1

OVER 子句 (Transact-SQL)

在应用关联的窗口函数之前确定行集的分区和排序。也就是说，OVER 子句在查询结果集中定义了一个窗口或用户指定的一组行。然后窗口函数为窗口中的每一行计算一个值。

Answer 2

使用group by：--

  SELECT CandEmail, MAX(CandName), MAX(EmployerId), MAX(ContNum), MAX(IsDeleted),          MAX(CandPortalId)
  FROM tbl1
  WHERE EmployerId = 7 AND IsDeleted = 0
  GROUP BY CandEmail

Answer 3

SELECT CandEmail, 
       MAX(CandName), 
       7 [EmployerId], 
       MAX(ContNum), 
       0 [IsDeleted], 
       MAX(CandPortalId)
FROM   tbl1
WHERE  EmployerId = 7 AND IsDeleted = 0
GROUP BY CandEmail

Answer 4

如果您不在乎ContNum得到哪个，那么您可以在该字段周围放置一个聚合函数，然后GROUP BY是其余部分：

SELECT CandEmail,
  CandName,
  EmployerId,
  MIN(ContNum) ContNum,  -- or you can use MAX()
  IsDeleted,
  CandPortalId 
FROM tbl1
WHERE EmployerId = 7 
  AND IsDeleted = 0
GROUP BY CandEmail,
  CandName,
  EmployerId, 
  IsDeleted,
  CandPortalId 

或者正如其他人指出的那样，您也应该在其他字段上使用聚合函数，除非您确定这些列中没有不同的值：

SELECT CandEmail,
  min(CandName) CandName,
  min(EmployerId) EmployerId,
  MIN(ContNum) ContNum,  -- or you can use MAX()
  min(IsDeleted) IsDeleted,
  min(CandPortalId) CandPortalId
FROM tbl1
WHERE EmployerId = 7 
  AND IsDeleted = 0
GROUP BY CandEmail