SQL查询从链接表中检索最后一条记录[重复]

Question

我编写了一个查询来比较不同表中的 2 列 (TRELAY VS TUSERDEF8)。该查询效果很好，只是它检索了TUSERDEF8 表中的顶部记录，该记录与TRELAY 表具有多对一关系。

这些表由TRELAY.ID = TUSERDEF8.N01 链接。我想从TUSERDEF8 检索最新记录并将该记录与TRELAY 记录进行比较。我打算使用索引列的最大值（TUSERDEF8.ID）来确定最新记录。

我正在使用 SQL Server。

我的代码如下，但我不确定如何更改查询以检索最后一个 TUSERDEF8 记录。任何帮助表示赞赏。

SELECT 
    TRELAY.ID, TRELAY.S15, 
    TUSERDEF8.S04, TUSERDEF8.N01, TUSERDEF8.S06
FROM 
    TRELAY
INNER JOIN 
    TUSERDEF8 ON TRELAY.ID = TUSERDEF8.N01
WHERE 
    LEFT(TRELAY.S15, 1) <> LEFT(TUSERDEF8.S04, 1)
    AND NOT (TRELAY.S15 LIKE '%MEDIUM%' AND
             TUSERDEF8.S04 LIKE '%N/A%' AND
             TUSERDEF8.S06 LIKE '%EACMS%')

Answer 1

假设您的 ID 是 int(s)，那么下面的方法可能有效吗？

SELECT TOP 1 TRELAY.ID, TRELAY.S15, TUSERDEF8.S04, TUSERDEF8.N01, TUSERDEF8.S06
FROM TRELAY INNER JOIN TUSERDEF8 
ON TRELAY.ID = TUSERDEF8.N01
WHERE LEFT(TRELAY.S15, 1) <> LEFT(TUSERDEF8.S04, 1)
AND NOT (
    TRELAY.S15 LIKE '%MEDIUM%' 
    AND TUSERDEF8.S04 LIKE '%N/A%' 
    AND TUSERDEF8.S06 LIKE '%EACMS%'
    )
ORDER BY TUSERDEF8.ID DESC

HTH

戴夫

Answer 2

你可以这样做：

With cteLastRecord As
(
Select  S04, N01, S06, 
        Row_Number() Over (Partition By N01, Order By ID Desc) SortOrder 
    From TUSERDEF8
)
SELECT 
    TRELAY.ID, TRELAY.S15, 
    TUSERDEF8.S04, TUSERDEF8.N01, TUSERDEF8.S06
FROM 
    TRELAY
INNER JOIN 
    (Select S04, N01, S06 From cteLastRecord Where SortOrder = 1) TUSERDEF8 ON TRELAY.ID = TUSERDEF8.N01
WHERE 
    LEFT(TRELAY.S15, 1) <> LEFT(TUSERDEF8.S04, 1)
    AND NOT (TRELAY.S15 LIKE '%MEDIUM%' AND
             TUSERDEF8.S04 LIKE '%N/A%' AND
             TUSERDEF8.S06 LIKE '%EACMS%')

Answer 3

我相信您的预期输出仍然有点模棱两可。

在我看来，您只需要 TUSERDEF8.ID 为最大值的输出中的记录。如果这是正确的，那么试试这个：

SELECT TRELAY.ID, TRELAY.S15, TUSERDEF8.S04, TUSERDEF8.N01, TUSERDEF8.S06
FROM TRELAY
  INNER JOIN TUSERDEF8 ON TRELAY.ID = TUSERDEF8.N01
WHERE LEFT(TRELAY.S15, 1) <> LEFT(TUSERDEF8.S04, 1)
  AND NOT (TRELAY.S15 LIKE '%MEDIUM%' AND
           TUSERDEF8.S04 LIKE '%N/A%' AND
           TUSERDEF8.S06 LIKE '%EACMS%')
  AND TUSERDEF8.ID IN (SELECT MAX(TUSERDEF8.ID) FROM TUSERDEF8)

编辑：在查看了您最近的 cmets 之后，看起来像这样的东西会更合适：

SELECT 
  , C.ID
  , C.S15, 
  , D.S04
  , D.N01
  , D.S06
FROM (
    SELECT A.ID, A.S15, MAX(B.ID) AS MaxID
    FROM TRELAY AS A
    INNER JOIN TUSERDEF8 AS B ON A.ID = B.N01
    WHERE 
    LEFT(A.S15, 1) <> LEFT(B.S04, 1)
    AND NOT (A.S15 LIKE '%MEDIUM%' AND
             B.S04 LIKE '%N/A%' AND
             B.S06 LIKE '%EACMS%')
    GROUP BY A.ID, A.S15
) AS C
INNER JOIN TUSERDEF8 AS D ON C.ID = D.N01 AND C.MaxID = D.ID

Answer 4

使用 ID 列来确定哪一行是“最后一行”是个坏主意

使用像“TUSERDEF8”这样的神秘表名（它与 TUSERDEF7 有什么不同）是一个非常糟糕的主意，同时使用像“S04”这样的完全神秘的列名。

对表格使用像“T”这样的前缀是个坏主意 - 应该已经很清楚它是一个表格。

现在所有这些都已经解决了：

SELECT 
    R.ID,
    R.S15,
    U.S04,
    U.N01,
    U.S06
FROM 
    TRELAY R
INNER JOIN TUSERDEF8 U ON U.N01 = R.ID
LEFT OUTER JOIN TUSERDEF8 U2 ON
    U2.N01 = R.ID AND
    U2.ID > U.ID
WHERE
    U2.ID IS NULL AND    -- This will only happen if the LEFT OUTER JOIN above found no match, meaning that the row in U has the highest ID value of all matches
    LEFT(R.S15, 1) <> LEFT(U.S04, 1) AND
    NOT (
        R.S15 LIKE '%MEDIUM%' AND
        U.S04 LIKE '%N/A%' AND
        U.S06 LIKE '%EACMS%'
    )