SQL：爲每個唯一密鑰選擇最大值？

Question

對不起，我不確定如何使用該語句，而且我對SQL的使用並不太好。數據庫引擎是SQL Server Compact。我現在有這個疑問：

SELECT * 
FROM Samples 
WHERE FunctionId NOT IN 
(SELECT CalleeId FROM Callers) 
ORDER BY ThreadId, HitCount DESC 

這給了我：

ThreadId Function HitCount 
     1  164  6945 
     1  3817   1 
     4  1328  7053 

現在，我只想與線程的每個唯一值的最大的命中計數結果。換句話說，應該放棄第二行。我不知道如何解決這個問題。

[編輯]如果有幫助，這是同一個查詢的另一種形式：

SELECT * 
FROM Samples s1 
LEFT OUTER JOIN Callers c1 
    ON s1.ThreadId = c1.ThreadId AND s1.FunctionId = c1.CalleeId 
WHERE c1.ThreadId IS NULL 
ORDER BY ThreadId 

[編輯]我最終使架構更改，以避免這樣做，因爲建議的查詢者望而昂貴。感謝所有的幫助。

Answer 1

SQL Server緊湊支持窗口函數嗎？

備選方案1 - 將包括所有打結的行。不包括行，如果給定線程的唯一行都有空的HitCount：

SELECT Thread, Function, HitCount 
FROM (SELECT Thread, Function, HitCount, 
     MAX(HitCount) over (PARTITION BY Thread) as MaxHitCount 
    FROM Samples 
    WHERE FunctionId NOT IN 
     (SELECT CalleeId FROM Callers)) t 
WHERE HitCount = MaxHitCount 
ORDER BY ThreadId, HitCount DESC 

方案2 - 將包括將所有行。如果沒有行，並與非空HitCount給定的線程，將返回所有行該線程：

SELECT Thread, Function, HitCount 
FROM (SELECT Thread, Function, HitCount, 
     RANK() over (PARTITION BY Thread ORDER BY HitCount DESC) as R 
    FROM Samples 
    WHERE FunctionId NOT IN 
     (SELECT CalleeId FROM Callers)) t 
WHERE R = 1 
ORDER BY ThreadId, HitCount DESC 

方案3 - 將非determistically挑領帶的情況下，一排並丟棄等。將包括行如果在一個線程中的所有行具有空HitCount

SELECT Thread, Function, HitCount 
FROM (SELECT Thread, Function, HitCount, 
     ROW_NUMBER() over (PARTITION BY Thread ORDER BY HitCount DESC) as R 
    FROM Samples 
    WHERE FunctionId NOT IN 
     (SELECT CalleeId FROM Callers)) t 
WHERE R = 1 
ORDER BY ThreadId, HitCount DESC 

替代4 & 5 - 使用舊的結構，如果窗口功能不可用，並說是什麼意思乾淨了一點比使用連接。基準如果spead是一個優先事項。兩者都返回參與平局的所有行。當非空值不適用於HitCount時，備選4將HitCount爲空。選項5不會返回HitCount爲空的行。

WITH maxHits AS(
    SELECT s.threadid, 
     MAX(s.hitcount) 'maxhits' 
    FROM SAMPLES s 
    JOIN CALLERS c ON c.threadid = s.threadid AND c.calleeid != s.functionid 
GROUP BY s.threadid 
) 
SELECT t.* 
    FROM SAMPLES t 
    JOIN CALLERS c ON c.threadid = t.threadid AND c.calleeid != t.functionid 
    JOIN maxHits mh ON mh.threadid = t.threadid AND mh.maxhits = t.hitcount 

任何數據庫的工作：

SELECT * 
FROM Samples s1 
WHERE FunctionId NOT IN 
    (SELECT CalleeId FROM Callers) 
AND NOT EXISTS 
    (SELECT * 
    FROM Samples s2 
    WHERE s1.FunctionId = s2.FunctionId 
    AND s1.HitCount < s2.HitCount) 
ORDER BY ThreadId, HitCount DESC 

SELECT * 
FROM Samples s1 
WHERE FunctionId NOT IN 
    (SELECT CalleeId FROM Callers) 
AND HitCount = 
    (SELECT MAX(HitCount) 
    FROM Samples s2 
    WHERE s1.FunctionId = s2.FunctionId) 
ORDER BY ThreadId, HitCount DESC 

Answer 2

這是我會怎麼做：

SELECT s1.* 
FROM Samples s1 
LEFT JOIN Samples s2 
    ON (s1.Thread = s2.Thread and s1.HitCount < s2.HitCount) 
WHERE s1.FunctionId NOT IN (SELECT CalleeId FROM Callers) 
    AND s2.Thread IS NULL 
ORDER BY s1.ThreadId, s1.HitCount DESC 

換句話說，該行s1對其中有沒有其他行s2匹配相同Thread而具有較大HitCount。

Answer 3

將與SQL Server 2005+工作

SELECT t.* 
    FROM SAMPLES t 
    JOIN CALLERS c ON c.threadid = t.threadid AND c.calleeid != t.functionid 
    JOIN (SELECT s.threadid, 
       MAX(s.hitcount) 'maxhits' 
      FROM SAMPLES s 
      JOIN CALLERS c ON c.threadid = s.threadid AND c.calleeid != s.functionid 
     GROUP BY s.threadid) mh ON mh.threadid = t.threadid AND mh.maxhits = t.hitcount