c# - 获取基于应该不同的一个字段的记录

Question

我有类似的查询

    SELECT distinct(a.CreatedOn),
       a.id AS ID ,
       u1.FirstName CreatedByFirstName,
       u1.LastName
FROM AuditDetail a
LEFT JOIN UserProfile u1 ON a.CreatedBy = u1.UserProfileID
LEFT JOIN UserProfile u2 ON a.UpdatedBy = u2.UserProfileID

这向我展示了所有的记录。并且 distinct createdon 也在每条记录中重复，因为所有记录都来了。我希望如果所有记录中的 createdon 都相同，那么它的第一条记录或单个记录不应该全部出现。我哪里错了？

Answer 1

试试这个，

可能会帮助你，使用子查询

SELECT a.CreatedOn,
       a.id AS ID ,
       u1.FirstName CreatedByFirstName,
       u1.LastName
FROM AuditDetail a
LEFT JOIN UserProfile u1 ON a.CreatedBy = u1.UserProfileID LEFT joinUserProfileu2 ON a.UpdatedBy = u2.UserProfileID
WHERE a.CreatedOn IN
    (SELECT DISTINCT CreatedOn
     FROM AuditDetail)

Answer 2

您可以使用Ranking Function诸如ROW_NUMBER()which 为每个组的每条记录提供排名。

WITH recordList
AS
(
    SELECT  a.CreatedOn,
            a.id as ID ,
            u1.FirstName CreatedByFirstName, 
            u1.LastName,
            ROW_NUMBER() OVER(PARTITION BY a.CreatedOn ORDER BY a.CreatedOn) rn
    FROM    AuditDetail a 
            left join UserProfile u1 
                on a.CreatedBy = u1.UserProfileID 
            left join UserProfile u2 
                on a.UpdatedBy = u2.UserProfileID
)
SELECT  CreatedOn,
        ID,
        CreatedByFirstName,
        LastName
FROM    recordList
WHERE   rn = 1