Question

我试图在同一行中返回多个记录值，所以我想对同一个表使用多个连接。我需要前两个记录并排显示。这些连接成为'LatestNote'和'SecondLatestNote'，使用RowNumber将它们分开。

非常简单的例子如下，但我没有得到任何结果。我在这里搞砸了什么？

带有不返回值的连接的SQL：

DECLARE @DateFrom AS DATETIME = CONVERT(DateTime, '2017-01-01 00:00:00.000', 120)
DECLARE @DateTo AS DATETIME = CONVERT(DateTime, '2018-01-01 00:00:00.000', 120)

SELECT
    LatestNote.NoteCode,
    LatestNote.NoteDate,           
    SecondLatestNote.NoteCode AS [NoteCode2nd],
    SecondLatestNote.NoteDate AS [NotDate2nd]

FROM Locations LOC


LEFT JOIN (
            SELECT TOP 2 LocationID, NoteID, Row_Number() OVER (ORDER BY Notedate DESC) AS RowNum
            FROM Notes(nolock) 
            WHERE NoteCode = 'NOTIFY' 
            AND NoteDate BETWEEN @DateFrom AND @DateTo
            ) 
                AS TopTwoNotes ON TopTwoNotes.LocationID = LOC.LocationID 

                LEFT JOIN Notes AS LatestNote ON LatestNote.NoteID = TopTwoNotes.NoteID AND TopTwoNotes.RowNum = 1

                LEFT JOIN Notes AS SecondLatestNote ON SecondLatestNote.NoteID = TopTwoNotes.NoteID AND TopTwoNotes.RowNum = 2 

WHERE LOC.LocationID = 308644

结果全为NULL，只返回一行，因为我正在使用LEFT JOIN。为什么这不起作用？

此SQL显示数据存在，结果如下：

SELECT TOP 2 LocationID, NoteID, Row_Number() OVER (ORDER BY NoteDate DESC) AS RowNum
            FROM Notes(nolock) 
            WHERE NoteCode = 'NOTIFY' 
            AND NoteDate BETWEEN @DateFrom AND @DateTo
            AND LocationID = 308644 

LocationID  NoteID  RowNum
308644  10291348    1
308644  10130566    2


SELECT
    NoteID,
    NoteCode,
    NoteDate,
    LEN(CAST(Note AS VARCHAR(8000))) AS [NoteCharCount]
FROM
    Notes
WHERE
    LocationID = 308644
    AND NoteDate BETWEEN @DateFrom AND @DateTo


NoteID  NoteCode    NoteDate    NoteCharCount
10130566    NOTIFY  2017-11-08  50
10291348    NOTIFY  2017-12-13  66

我必须遗漏一些东西 - 我不能像这样使用rownum加入吗？

感谢您的帮助。

Answer 1

您需要在子查询的where子句中添加条件LocationID = 308644，否则第一行和第二行可能不包含LocationID = 308644。

然后您使用与LEFT JOIN不匹配的LocationID = 308644，因此会NULL行。

SELECT LatestNote.notecode, 
       LatestNote.notedate, 
       SecondLatestNote.notecode AS [NoteCode2nd], 
       SecondLatestNote.notedate AS [NotDate2nd] 
FROM   locations LOC 
       LEFT JOIN (SELECT TOP 2 locationid, 
                               noteid, 
                               Row_number() 
                                 OVER ( 
                                   ORDER BY notedate DESC) AS RowNum 
                  FROM   notes(nolock) 
                  WHERE  notecode = 'NOTIFY' 
                         AND notedate BETWEEN @DateFrom AND @DateTo AND LocationID = 308644) AS TopTwoNotes 
              ON TopTwoNotes.locationid = LOC.locationid 
       LEFT JOIN notes AS LatestNote 
              ON LatestNote.noteid = TopTwoNotes.noteid 
                 AND TopTwoNotes.rownum = 1 
       LEFT JOIN notes AS SecondLatestNote 
              ON SecondLatestNote.noteid = TopTwoNotes.noteid 
                 AND TopTwoNotes.rownum = 2 
WHERE  LOC.locationid = 308644

修改

您可以在子查询上放locations表LEFT JOIN。

SELECT LatestNote.notecode, LatestNote.notedate, SecondLatestNote.notecode AS [NoteCode2nd], SecondLatestNote.notedate AS [NotDate2nd] FROM ( SELECT TOP 2 TopTwoNotes.locationid, TopTwoNotes.noteid, Row_number() OVER (ORDER BY TopTwoNotes.notedate DESC) AS RowNum FROM locations LOC LEFT JOIN notes(nolock) TopTwoNotes ON TopTwoNotes.locationid = LOC.locationid WHERE TopTwoNotes.notecode = 'NOTIFY' AND TopTwoNotes.notedate BETWEEN @DateFrom AND @DateTo AND LOC.locationid = 308644 ORDER BY TopTwoNotes.notedate DESC ) AS TopTwoNotes INNER JOIN notes AS LatestNote ON LatestNote.noteid = TopTwoNotes.noteid AND TopTwoNotes.rownum = 1 INNER JOIN notes AS SecondLatestNote ON SecondLatestNote.noteid = TopTwoNotes.noteid AND TopTwoNotes.rownum = 2

Answer 2

您可以使用System.out.println("The Longest String is: " + longString + " With The Index Of" + java.util.Arrays.asList(names).indexOf(longString));解决此问题：

apply

使用rownum的SQL Server同行连接不返回值

2 个答案: