JOIN table when selecting a max value of columns

Question

I have the below table structure that is successfully getting the max column value of a table for each CommentID . But I want to JOIN the table tbComment with tbCommentBreadcrumb where CommentID is the key.

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

Here's what I have working:

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

This returns over a hundred records and I want to further refine the query by only getting the records where the above query is true but also that each of the CommentID in the table tbComment is locked. Basically not sure where to JOIN tbComment and put the AND tbComment.CommentIsLocked = 1

Answer 1

You are quite close :-)

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

Answer 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