Select 具有最大 ID 和特定条件的行

Question

我有一个 table 具有以下结构的评论：

CommentId (int), 
CommentText (nvarchar(max))
EditedBy (nvarchar(max))
ParentCommentId (int)
CaseId (int)

对于特定的 caseId 我想要 select 最新的评论文本以及 EditedBy 专栏。

例如，如果有人添加评论 table 将是

CommentId   CommentText          EditedBy     ParentCommentId   CaseId
   1         ParentComment1         ABC          NULL               1 
   2         ParentComment2         ABC          NULL               1

现在，如果有人编辑该评论，table 将看起来像

CommentId   CommentText          EditedBy     ParentCommentId   CaseId
   1         ParentComment1       ABC          NULL               1 
   2         ParentComment2       ABC          NULL               2
   3         Comment2             DEF          1                  1

此编辑可以进行任意次数我想 select 最新的评论以及历史。在这种情况下，我的数据集应该是这样的：

CaseId   CommentId   CommentText       Predicate
  1       3           Comment2         Created By ABC , Updated by DEF
  1       2           ParentComment2   Created By ABC

这是问题的简化版本。 TIA

Answer 1

您可以使用 FOR XML PATH 创建谓词列。像这样。

SQL Fiddle

示例数据

CREATE TABLE Comment
    ([CommentId] int, [CommentText] varchar(8), [EditedBy] varchar(3), [ParentCommentId] varchar(4), [CaseId] int);

INSERT INTO Comment
    ([CommentId], [CommentText], [EditedBy], [ParentCommentId], [CaseId])
VALUES
    (1, 'Comment1', 'ABC', NULL, 1),
    (2, 'Comment2', 'DEF', '1', 1);

查询

;WITH CTE AS 
(
SELECT CommentID, CommentText,EditedBy,ParentCommentID,CaseID,ROW_NUMBER()OVER(PARTITION BY Caseid ORDER BY CommentID DESC) RN
FROM Comment
), CTE2 as
(
SELECT CommentID, CommentText,EditedBy,ParentCommentID,CaseID,
  (
    SELECT
    CASE WHEN ParentCommentID IS NULL THEN 'Created By ' ELSE ', Updated By ' END
    + EditedBy
    FROM CTE C1
    WHERE C1.CaseID = C2.CaseID
    ORDER BY CommentID ASC
    FOR XML PATH('')
  ) as Predicate
FROM CTE C2
WHERE RN = 1
)
SELECT CaseID,CommentID, CommentText,Predicate FROM CTE2;

编辑

如果您不想为每个更新 caseid 的用户重复 Updated By，请使用以下 CASE

CASE WHEN ParentCommentID IS NULL THEN 'Created By ' + EditedBy + ', Updated By' ELSE '' END,
CASE WHEN ParentCommentID IS NOT NULL THEN ', ' + EditedBy ELSE '' END

而不是

    CASE WHEN ParentCommentID IS NULL THEN 'Created By ' ELSE ', Updated By ' END + EditedBy

输出

| CaseID | CommentID | CommentText |                      Predicate |
|--------|-----------|-------------|--------------------------------|
|      1 |         2 |    Comment2 | Created By ABC, Updated By DEF |

编辑 2

使用递归 CTE 实现您的预期输出。像这样。

SQL Fiddle

查询

;WITH CTEComment AS 
(
SELECT CommentID as RootCommentID,CommentID, CommentText,EditedBy,ParentCommentID,CaseID
FROM Comment
WHERE ParentCommentID IS NULL
UNION ALL 
SELECT CTEComment.RootCommentID as RootCommentID,Comment.CommentID, Comment.CommentText,Comment.EditedBy,Comment.ParentCommentID,Comment.CaseID
FROM CTEComment
INNER JOIN Comment
    ON CTEComment.CommentID = Comment.ParentcommentID
        AND CTEComment.CaseID = Comment.CaseID
), CTE as  
(
SELECT CommentID,RootCommentID,CommentText,EditedBy,ParentCommentID,CaseID,ROW_NUMBER()OVER(PARTITION BY CaseID,RootCommentID ORDER BY CommentID DESC) RN
FROM CTEComment
), CTE2 as
(
SELECT CommentID, CommentText,EditedBy,ParentCommentID,CaseID,
  (
    SELECT
    CASE WHEN ParentCommentID IS NULL THEN 'Created By ' ELSE ', Updated By ' END
    + EditedBy
    FROM CTE C1
    WHERE C1.CaseID = C2.CaseID
    AND C1.RootCommentID = C2.RootCommentID
    ORDER BY CommentID ASC
    FOR XML PATH('')
  ) as Predicate
FROM CTE C2
WHERE RN = 1
)
SELECT CaseID,CommentID, CommentText,Predicate FROM CTE2;

输出

| CaseID | CommentID |    CommentText |                      Predicate |
|--------|-----------|----------------|--------------------------------|
|      1 |         3 |       Comment2 | Created By ABC, Updated By DEF |
|      2 |         2 | ParentComment2 |                 Created By ABC |

Answer 2

You can use this method
DECLARE @CaseId [int];
SET @CaseId=1`enter code here`
DECLARE @GeneratedBy [nvarchar](max);
SET @GeneratedBy=(SELECT  EditBy from Comment  WHERE ParentCommentId is NULL AND CaseId = @CaseId)
PRINT @GeneratedBy;
SELECT CaseId , CommentId , CommentText  , 'Created By '+@GeneratedBy+ ', Updated By ' +EditBy  AS Predicate FROM Comment
WHERE CaseId = @CaseId AND ParentCommentId=(SELECT  max(ParentCommentId) from Comment  WHERE  CaseId = @CaseId)

Answer 3

您可以简单地使用自联接来获得结果：

找到下面的查询：

select a.CaseId,b.CommentId, b.CommentText,'Created By '+a.EditedBy +', update by '+b.EditedBy as Predicate
from Comment a
inner join Comment b
on a.CaseId=b.CaseId
where a.CommentId<b.CommentId

Select 具有最大 ID 和特定条件的行

Select the row with the biggest ID and a specific condition

sql

sql-server

select

greatest-n-per-group