sql - これが最新のメッセージでソートされていないのはなぜですか

Question

SELECT TOP (100) PERCENT MsgCount.msgcount
    , c.userid
    , c.aspnet_guid
    , c.fname
    , c.lname
    , c.profileimagepath
    , c.profilealbumid
    , p1.msgdate
    , SUBSTRING(p1.msgcontent, 0, 50) AS msgcontent
    , p1.msgtouser
FROM dbo.userprofile AS c 
INNER JOIN dbo.usermessages AS p1 
    ON c.userid = p1.msgfromuser 
LEFT OUTER JOIN dbo.usermessages AS p2 
    ON c.userid = p2.msgfromuser 
    AND (p1.msgdate < p2.msgdate 
          OR p1.msgdate = p2.msgdate 
          AND p1.msgid < p2.msgid) 
LEFT OUTER JOIN  
(
    SELECT msgfromuser
        , COUNT(msgfromuser) AS msgcount
    FROM dbo.usermessages
    GROUP BY msgfromuser
) AS MsgCount 
    ON MsgCount.msgfromuser = p1.msgfromuser
WHERE     (p2.msgid IS NULL)
ORDER BY p2.msgdate DESC

Answer 1

多分次のように注文してみてください：

p1.msgdate

それ以外の：

p2.msgdate

これは単なる提案です:)

Answer 2

あなたのテーブルでデータがどのように見えるかはわかりませんが、p2 への左外部結合があるため、値がなく、p2.msgdate が null であることが予想されると思います。p2.msgdate (null 列の可能性がある) だけで順序付けすると、常に値を持つ列で順序付けする場合とは異なり、一貫した結果が得られません。おそらく、p1.msgdate で並べ替えたり、coalesce(p2.msgdate,p1.msgdate) で並べ替えたりすると、より一貫した結果が得られる場合があります。

SELECT TOP (100) PERCENT MsgCount.msgcount
    , c.userid
    , c.aspnet_guid
    , c.fname
    , c.lname
    , c.profileimagepath
    , c.profilealbumid
    , p1.msgdate
    , SUBSTRING(p1.msgcontent, 0, 50) AS msgcontent
    , p1.msgtouser
FROM dbo.userprofile AS c 
INNER JOIN dbo.usermessages AS p1 
    ON c.userid = p1.msgfromuser 
LEFT OUTER JOIN dbo.usermessages AS p2 
    ON c.userid = p2.msgfromuser 
    AND (p1.msgdate < p2.msgdate 
          OR p1.msgdate = p2.msgdate 
          AND p1.msgid < p2.msgid) 
LEFT OUTER JOIN  
(
    SELECT msgfromuser
        , COUNT(msgfromuser) AS msgcount
    FROM dbo.usermessages
    GROUP BY msgfromuser
) AS MsgCount 
    ON MsgCount.msgfromuser = p1.msgfromuser
WHERE     (p2.msgid IS NULL)
ORDER BY p1.msgdate, p2.msgdate DESC