选择列的最大值时加入表

Posted 2023-04-18

【中文标题】选择列的最大值时加入表

【英文标题】：JOIN table when selecting a max value of columns

【发布时间】：2014-02-09 20:04:31

【问题描述】：

我有下面的表结构，它成功地获取了每个CommentID 的表的最大列值。但我想用tbCommentBreadcrumb 加入表tbComment，其中CommentID 是关键。

tbComment

CommentID     IsLocked
1             0      
2             0
3             1
4             0
5             1

tbCommentBreadcrumb

CommentStatusID  CommentID   StatusTypeID
105              1           1                
106              1           4                
107              2           1                
108              3           1               
109              3           4
110              4           1 
112              5           1
112              5           4

这是我的工作：

SELECT *
FROM
(
   SELECT
     *,
     ROW_NUMBER() OVER (PARTITION BY CommentID ORDER BY CreateDateTime desc) as rn
   FROM
     tbCommentBreadCrumb
   WHERE 
     CommentStatusTypeID = 4
     AND CreateDateTime <= ts '2014-02-09 09:44:57'
) t
WHERE
   t.rn = 1
ORDER BY 
   CommentStatusID DESC

这将返回一百多条记录，我想通过仅获取上述查询为真但表tbComment 中的每个CommentID 被锁定的记录来进一步细化查询。基本上不知道在哪里加入tbComment并把AND tbComment.CommentIsLocked = 1放在哪里

【参考方案1】：

你很亲密:-)

SELECT t.*
FROM
(
   SELECT
     *,
     ROW_NUMBER() OVER (PARTITION BY CommentID ORDER BY CreateDateTime desc) as rn
   FROM
     tbCommentBreadCrumb
     WHERE CommentStatusTypeID = 4
            AND    CreateDateTime <= ts '2014-02-09 09:44:57'
) t
JOIN tbComment c ON t.CommentID = c.CommentID
WHERE
   t.rn = 1
AND c.CommentIsLocked = 1
ORDER BY CommentStatusID DESC

【参考方案2】：

;With CTE
AS
(
   SELECT *,
       ROW_NUMBER() OVER (PARTITION BY CommentID ORDER BY CreateDateTime desc) as rn
   FROM  tbCommentBreadCrumb
   WHERE CommentStatusTypeID = 4
   AND   CreateDateTime <= ts '2014-02-09 09:44:57'
) 
SELECT * 
FROM CTE C INNER JOIN tbComment TC
ON C.CommentID = TC.CommentID   
WHERE  C.rn = 1
ORDER BY C.CommentStatusID DESC