SQL查詢非常慢，需要改進

-4

我有一個選擇查詢，我需要改進才能使其更快。SQL查詢非常慢，需要改進

SELECT 
    st.SigHistUID, st.RelationType, st2.RelationType, 
    case 
     when st.RelationType <> st2.RelationType 
      then 'N' 
      else st.RelationType 
    end as [NewRelationType], 
    st.ToSigUID , sh.FullDescription, sh.SigHistUID AS ToSigHistUID 
FROM 
    [Stackability] (nolock) st 
INNER JOIN 
    [SignatureHistory] (nolock) sh ON sh.SigUID = st.ToSigUID 
            AND sh.SigHistUID = (SELECT TOP 1 SigHistUID FROM [SignatureHistory] (nolock) tmp where tmp.SigUID = sh.SigUID ORDER BY SigHistUID DESC) 
INNER JOIN 
    [SignatureHistory] (nolock) sh2 ON st.SigHistUID = sh2.SigHistUID 
INNER JOIN 
    Stackability (nolock) st2 on st2.ToSigUID = sh2.SigUID and st2.SigHistUID = sh.SigHistUID 
WHERE 
    st.SigHistUID < 1000 and 
    st.RelationType <> st2.RelationType 
ORDER BY 
    st.SigHistUID

來源

2017-06-29 N. Leroy

這是**得太少**信息！什麼是桌子結構？這些表上定義了什麼樣的索引？每張桌子都有哪些數據（以**爲單位）？ –

你應該[至少包括實際的執行計劃]（https://stackoverflow.com/a/7359705/1260204），你可以使用[粘貼計劃]（https://www.brentozar.com/pastetheplan /）並在你的問題中分享鏈接。另外[嘗試自己讀]（https://stackoverflow.com/a/759097/1260204），也許你可以找出與您的查詢性能問題（S）。最後，包括[schema ddl]（https://en.wikipedia.org/wiki/Data_definition_language）以及您正在執行的查詢。 – Igor

根據SignatureHistory的大小，由於子查詢結果未被編入索引，子查詢可能會在sh連接上減慢速度。也許找到一種方法來避免該子查詢。 – justiceorjustus

嘗試有取出頂部1條件：

SELECT 
    st.SigHistUID, st.RelationType, st2.RelationType, 
    case 
     when st.RelationType <> st2.RelationType 
      then 'N' 
      else st.RelationType 
    end as [NewRelationType], 
    st.ToSigUID , sh.FullDescription, sh.SigHistUID AS ToSigHistUID 
FROM 
    [Stackability] (nolock) st 
INNER JOIN 
    (select distinct siguid, max(SigHistUID) OVER(PARTITION BY siguid) as SigHistUID from [SignatureHistory] (nolock)) sh ON sh.SigUID = st.ToSigUID 

INNER JOIN 
    [SignatureHistory] (nolock) sh2 ON st.SigHistUID = sh2.SigHistUID 
INNER JOIN 
    Stackability (nolock) st2 on st2.ToSigUID = sh2.SigUID and st2.SigHistUID = sh.SigHistUID 
WHERE 
    st.SigHistUID < 1000 and 
    st.RelationType <> st2.RelationType 
ORDER BY 
    st.SigHistUID

來源

2017-06-29 15:50:49 cloudsafe

非常感謝大家。 –

SQL查詢非常慢，需要改進

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