什麼性能更好：UNION查詢和separete查詢的一堆？

我有一個自定義商店網站，當他/她按下購買按鈕時，使用一組規則（更準確地說是7）來爲用戶定位零件。有些規則是這樣的：什麼性能更好：UNION查詢和separete查詢的一堆？

查找第一銷售者在同一國家，市，區爲消費者（每區只有一個賣家是允許的）
如果賣方上面沒有部分，得到與上述同一組的賣家，並在同一城市
如果上述賣家沒有該零件，得到一個賣家在同一城市
等等。。

我已經制定了一個ser並且每個規則的巨大聯盟中有大約300行SQL（格式化爲便於閱讀），只有第一個結果才能找到。

我不確定這是更好的事情要做還是更好地做7順序檢查有條件的往返行程，如果後面的一個在調用下一個結果之前有結果。

我估計大部分用戶都會經歷規則4，即SQL Server的4次往返，只是爲了得到一個部分，並且巨型聯合查詢的結果在不到一秒內返回，少於100,000個部分表。

問題是，如果這個網站開始在可用部件和用戶的溫度下長大，那麼最好是讓SQL Server處理帶有巨大查詢的工作，該查詢只返回我在一次旅行中需要的或者更好調用單獨的查詢？

我們使用傳統的ASP來完成這項工作（是的，老學校，你知道嗎？）如果這在任何情況下都是相關的。

讓我知道你是否需要查看查詢本身。

編輯：

只是爲了總之，這裏是我現在使用的查詢：

SELECT TOP 1 regras.ids, regras.idCadastro, regras.regra, e.descricao AS nomeEstado, cd.descricao AS nomeCidade, b.nome AS nomeBairro 
FROM ( 
    SELECT dbo.group_concat(idPecaItem) AS ids, idCadastro, '1' AS regra 
    FROM ( 
     SELECT TOP 2 idPecaItem, idCadastro 
     FROM pecasItens 
     WHERE COALESCE(pecasItens.idCadastro, 0) = (CASE WHEN EXISTS( 
      SELECT TOP 1 COALESCE(pi.idCadastro, 0) 
      FROM pecasItens pi 
      LEFT JOIN cadastros c ON pi.idCadastro = c.idCadastro 
      WHERE (pi.idCadastro IS NULL OR c.tipoParceiro = 'c') AND idPeca = 31740 AND idPedidoItem IS NULL AND dataEntrada <= '2014-3-13' AND devolucaoSolicitada IS NULL 
      GROUP BY pi.idCadastro 
      HAVING COUNT(pi.idPecaItem) >= 2 
     ) THEN ( 
      SELECT TOP 1 COALESCE(pi.idCadastro, 0) 
      FROM pecasItens pi 
      LEFT JOIN cadastros c ON pi.idCadastro = c.idCadastro 
      WHERE (pi.idCadastro IS NULL OR c.tipoParceiro = 'c') AND idPeca = 31740 AND idPedidoItem IS NULL AND dataEntrada <= '2014-3-13' AND devolucaoSolicitada IS NULL 
      GROUP BY pi.idCadastro 
      HAVING COUNT(pi.idPecaItem) >= 2 
     ) ELSE NULL END) 
     AND idPeca = 31740 AND idPedidoItem IS NULL AND dataEntrada <= '2014-3-13' AND devolucaoSolicitada IS NULL 
    ) regra1 
    GROUP BY idCadastro 

    UNION 

    SELECT dbo.group_concat(idPecaItem) AS ids, idCadastro, '2' AS regra 
    FROM ( 
     SELECT TOP 2 idPecaItem, idCadastro 
     FROM pecasItens 
     WHERE COALESCE(pecasItens.idCadastro, 0) = (CASE WHEN EXISTS( 
      SELECT TOP 1 COALESCE(pi.idCadastro, 0) 
      FROM pecasItens pi 
      LEFT JOIN cadastros c ON pi.idCadastro = c.idCadastro AND c.tipoParceiro = 'r' AND c.idCadastroGrupo = 1 
      WHERE pi.idCadastro IS NOT NULL AND idPeca = 31740 AND idPedidoItem IS NULL AND dataEntrada <= '2014-3-13' AND devolucaoSolicitada IS NULL 
      GROUP BY pi.idCadastro 
      HAVING COUNT(pi.idPecaItem) >= 2 
     ) THEN ( 
      SELECT TOP 1 COALESCE(pi.idCadastro, 0) 
      FROM pecasItens pi 
      LEFT JOIN cadastros c ON pi.idCadastro = c.idCadastro AND c.tipoParceiro = 'r' AND c.idCadastroGrupo = 1 
      WHERE pi.idCadastro IS NOT NULL AND idPeca = 31740 AND idPedidoItem IS NULL AND dataEntrada <= '2014-3-13' AND devolucaoSolicitada IS NULL 
      GROUP BY pi.idCadastro 
      HAVING COUNT(pi.idPecaItem) >= 2 
     ) ELSE NULL END) 
     AND idPeca = 31740 AND idPedidoItem IS NULL AND dataEntrada <= '2014-3-13' AND devolucaoSolicitada IS NULL 
    ) regra2 
    GROUP BY idCadastro 

    UNION 

    SELECT dbo.group_concat(idPecaItem) AS ids, idCadastro, '3' AS regra 
    FROM ( 
     SELECT TOP 2 idPecaItem, idCadastro 
     FROM pecasItens 
     WHERE COALESCE(pecasItens.idCadastro, 0) = (CASE WHEN EXISTS( 
      SELECT TOP 1 COALESCE(pi.idCadastro, 0) 
      FROM pecasItens pi 
      LEFT JOIN cadastros c ON pi.idCadastro = c.idCadastro AND c.tipoParceiro = 'r' AND c.idCadastroGrupo = 1 
      INNER JOIN cadastrosCidades cc ON c.idCadastro = cc.idCadastro AND cc.idCidade = 4850 
      WHERE pi.idCadastro IS NOT NULL AND idPeca = 31740 AND idPedidoItem IS NULL AND dataEntrada <= '2014-3-13' AND devolucaoSolicitada IS NULL 
      GROUP BY pi.idCadastro 
      HAVING COUNT(pi.idPecaItem) >= 2 
     ) THEN ( 
      SELECT TOP 1 COALESCE(pi.idCadastro, 0) 
      FROM pecasItens pi 
      LEFT JOIN cadastros c ON pi.idCadastro = c.idCadastro AND c.tipoParceiro = 'r' AND c.idCadastroGrupo = 1 
      INNER JOIN cadastrosCidades cc ON c.idCadastro = cc.idCadastro AND cc.idCidade = 4850 
      WHERE pi.idCadastro IS NOT NULL AND idPeca = 31740 AND idPedidoItem IS NULL AND dataEntrada <= '2014-3-13' AND devolucaoSolicitada IS NULL 
      GROUP BY pi.idCadastro 
      HAVING COUNT(pi.idPecaItem) >= 2 
     ) ELSE NULL END) 
     AND idPeca = 31740 AND idPedidoItem IS NULL AND dataEntrada <= '2014-3-13' AND devolucaoSolicitada IS NULL 
    ) regra3 
    GROUP BY idCadastro 
    UNION 

    SELECT dbo.group_concat(idPecaItem) AS ids, idCadastro, '4' AS regra 
    FROM ( 
     SELECT TOP 2 idPecaItem, idCadastro 
     FROM pecasItens 
     WHERE COALESCE(pecasItens.idCadastro, 0) = (CASE WHEN EXISTS( 
      SELECT TOP 1 COALESCE(pi.idCadastro, 0) 
      FROM pecasItens pi 
      INNER JOIN cadastros c ON pi.idCadastro = c.idCadastro AND c.tipoParceiro = 'r' 
      INNER JOIN cadastrosGrupos cg ON c.idCadastroGrupo = cg.idCadastroGrupo AND cg.idMarca = 2 
      INNER JOIN cadastrosCidades cc ON c.idCadastro = cc.idCadastro AND cc.idCidade = 4850 
      WHERE pi.idCadastro IS NOT NULL AND idPeca = 31740 AND idPedidoItem IS NULL AND dataEntrada <= '2014-3-13' AND devolucaoSolicitada IS NULL 
      GROUP BY pi.idCadastro 
      HAVING COUNT(pi.idPecaItem) >= 2 
     ) THEN ( 
      SELECT TOP 1 COALESCE(pi.idCadastro, 0) 
      FROM pecasItens pi 
      INNER JOIN cadastros c ON pi.idCadastro = c.idCadastro AND c.tipoParceiro = 'r' 
      INNER JOIN cadastrosGrupos cg ON c.idCadastroGrupo = cg.idCadastroGrupo AND cg.idMarca = 2 
      INNER JOIN cadastrosCidades cc ON c.idCadastro = cc.idCadastro AND cc.idCidade = 4850 
      WHERE pi.idCadastro IS NOT NULL AND idPeca = 31740 AND idPedidoItem IS NULL AND dataEntrada <= '2014-3-13' AND devolucaoSolicitada IS NULL 
      GROUP BY pi.idCadastro 
      HAVING COUNT(pi.idPecaItem) >= 2 
     ) ELSE NULL END) 
     AND idPeca = 31740 AND idPedidoItem IS NULL AND dataEntrada <= '2014-3-13' AND devolucaoSolicitada IS NULL 
    ) regra4 
    GROUP BY idCadastro 

    UNION 

    SELECT dbo.group_concat(idPecaItem) AS ids, idCadastro, '5' AS regra 
    FROM ( 
     SELECT TOP 2 idPecaItem, idCadastro 
     FROM pecasItens 
     WHERE COALESCE(pecasItens.idCadastro, 0) = (CASE WHEN EXISTS( 
      SELECT TOP 1 COALESCE(pi.idCadastro, 0) 
      FROM pecasItens pi 
      INNER JOIN cadastrosGrupos cg ON pi.idCadastro = cg.idCadastroMontadora AND cg.idCadastroGrupo = 1 
      WHERE pi.idCadastro IS NOT NULL AND idPeca = 31740 AND idPedidoItem IS NULL AND dataEntrada <= '2014-3-13' AND devolucaoSolicitada IS NULL 
      GROUP BY pi.idCadastro 
      HAVING COUNT(pi.idPecaItem) >= 2 
     ) THEN ( 
      SELECT TOP 1 COALESCE(pi.idCadastro, 0) 
      FROM pecasItens pi 
      INNER JOIN cadastrosGrupos cg ON pi.idCadastro = cg.idCadastroMontadora AND cg.idCadastroGrupo = 1 
      WHERE pi.idCadastro IS NOT NULL AND idPeca = 31740 AND idPedidoItem IS NULL AND dataEntrada <= '2014-3-13' AND devolucaoSolicitada IS NULL 
      GROUP BY pi.idCadastro 
      HAVING COUNT(pi.idPecaItem) >= 2 
     ) ELSE NULL END) 
     AND idPeca = 31740 AND idPedidoItem IS NULL AND dataEntrada <= '2014-3-13' AND devolucaoSolicitada IS NULL 
    ) regra5 
    GROUP BY idCadastro 

    UNION 

    SELECT dbo.group_concat(idPecaItem) AS ids, idCadastro, '6' AS regra 
    FROM ( 
     SELECT TOP 2 idPecaItem, idCadastro 
     FROM pecasItens 
     WHERE COALESCE(pecasItens.idCadastro, 0) = (CASE WHEN EXISTS( 
      SELECT TOP 1 COALESCE(pi.idCadastro, 0) 
      FROM pecasItens pi 
      LEFT JOIN cadastros c ON pi.idCadastro = c.idCadastro AND c.tipoParceiro = 'r' AND c.idEstado = 25 AND c.atendeEstadoTodo = 1 
      WHERE pi.idCadastro IS NOT NULL AND idPeca = 31740 AND idPedidoItem IS NULL AND dataEntrada <= '2014-3-13' AND devolucaoSolicitada IS NULL 
      GROUP BY pi.idCadastro 
      HAVING COUNT(pi.idPecaItem) >= 2 
     ) THEN ( 
      SELECT TOP 1 COALESCE(pi.idCadastro, 0) 
      FROM pecasItens pi 
      LEFT JOIN cadastros c ON pi.idCadastro = c.idCadastro AND c.tipoParceiro = 'r' AND c.idEstado = 25 AND c.atendeEstadoTodo = 1 
      WHERE pi.idCadastro IS NOT NULL AND idPeca = 31740 AND idPedidoItem IS NULL AND dataEntrada <= '2014-3-13' AND devolucaoSolicitada IS NULL 
      GROUP BY pi.idCadastro 
      HAVING COUNT(pi.idPecaItem) >= 2 
     ) ELSE NULL END) 
     AND idPeca = 31740 AND idPedidoItem IS NULL AND dataEntrada <= '2014-3-13' AND devolucaoSolicitada IS NULL 
    ) regra6 
    GROUP BY idCadastro 

    UNION 

    SELECT dbo.group_concat(idPecaItem) AS ids, idCadastro, '7' AS regra 
    FROM ( 
     SELECT TOP 2 idPecaItem, idCadastro 
     FROM pecasItens 
     WHERE COALESCE(pecasItens.idCadastro, 0) = (CASE WHEN EXISTS( 
      SELECT TOP 1 COALESCE(pi.idCadastro, 0) 
      FROM pecasItens pi 
      LEFT JOIN cadastros c ON pi.idCadastro = c.idCadastro AND c.tipoParceiro = 'r' AND c.atendeBrasilTodo = 1 
      WHERE pi.idCadastro IS NOT NULL AND idPeca = 31740 AND idPedidoItem IS NULL AND dataEntrada <= '2014-3-13' AND devolucaoSolicitada IS NULL 
      GROUP BY pi.idCadastro 
      HAVING COUNT(pi.idPecaItem) >= 2 
     ) THEN ( 
      SELECT TOP 1 COALESCE(pi.idCadastro, 0) 
      FROM pecasItens pi 
      LEFT JOIN cadastros c ON pi.idCadastro = c.idCadastro AND c.tipoParceiro = 'r' AND c.atendeBrasilTodo = 1 
      WHERE pi.idCadastro IS NOT NULL AND idPeca = 31740 AND idPedidoItem IS NULL AND dataEntrada <= '2014-3-13' AND devolucaoSolicitada IS NULL 
      GROUP BY pi.idCadastro 
      HAVING COUNT(pi.idPecaItem) >= 2 
     ) ELSE NULL END) 
     AND idPeca = 31740 AND idPedidoItem IS NULL AND dataEntrada <= '2014-3-13' AND devolucaoSolicitada IS NULL 
    ) regra7 
    GROUP BY idCadastro 
) regras 
LEFT JOIN cadastros c ON regras.idCadastro = c.idCadastro 
LEFT JOIN listaEstados e ON c.idEstado = e.idEstado 
LEFT JOIN listaCidades cd ON c.idCidade = cd.idCidade 
LEFT JOIN listaBairros b ON c.idBairro = b.idBairro 
ORDER BY regra ASC

不，這不是MySQL的。 group_concat()這裏是來自這個人的自定義聚合http://groupconcat.codeplex.com/

來源

2014-03-07 rcdmk

您如何看待，現在是否有必要查看查詢？ – Alexander

對不起。我沒有得到它。英語不是我的母語。我想你很諷刺，並告訴我發佈查詢。是對的，有趣嗎？ – rcdmk

小心過早優化（「http://c2.com/cgi/wiki?PrematureOptimization」）！但無論如何，不妨考慮一下。以這種方式想想......你有兩個選擇，所以如果它成爲瓶頸，你可以在流程中間切換你的過程。可選性在這裏很好。我傾向於將這些推到一個聯合中，特別是如果底層查詢只能在這種情況下使用。第三種選擇是將過濾的記錄集（Sql很棒）返回到100條左右的記錄，並在代碼中進行決策（並且單元測試您如何做出決定）。 – BlackjacketMack

在幾乎所有情況下，RDBMS都處於一個更好的位置，可以讓你成爲第一行。

如果您的查詢看起來像這樣，

SELECT TOP 1 * 
FROM (
    SELECT ... FROM ... -- Query #1 
UNION ALL 
    SELECT ... FROM ... -- Query #2 
UNION ALL 
    ... 
UNION ALL 
    SELECT ... FROM ... -- Query #7 
)

優化是足夠聰明的停止詢問在什麼是產生你所需要的結果的規則，是它的規則一，規則四或規則七。最重要的是，優化器可以並行運行您的查詢。因爲它離你的數據更近，所以很難想象你可以通過將部分查詢邏輯從你的RDBMS中移走來「超越」它。

來源

2014-03-07 13:36:30 dasblinkenlight

謝謝，我就是這麼做的。我很好奇，如果在併發訪問數量增長時這不會影響性能，但不知道優化程序在找到結果時停止。很高興知道。 – rcdmk

您能否澄清我更多？這些查詢按執行順序返回嗎？可以說我有'選擇top 1 * from（選擇x，1作爲q從tbl，其中y = 1聯合選擇x，2作爲q從tbl，其中y = 2）tb order by q asc'。是否需要訂單來保證規則將按順序返回，否則這隻會導致更多的性能損失？ – rcdmk

@rcdmk「UNION」的順序不能保證 - 您可以以任意順序獲取數據，對於相同的RDBMS甚至可能不會相同。良好的優化器可以並行運行各個SELECT，因此您可以獲得「贏得比賽」的排名。添加一個ORDER BY'不會改變任何東西，因爲它會應用於查詢的結果，這是一行。 – dasblinkenlight

我的傾向是將工作留在SQL中，但重構您的查詢，因此它不是聯合。您應該能夠提供一個存儲過程，一旦找到結果，內部會執行一系列單個查詢。僞SQL將會像這樣開始，並可能在此過程中得到改進。

CREATE PROC GetBestSeller (Part, State, City, District) AS BEGIN 

    DECLARE @Seller INT 

    SELECT TOP 1 @idSeller = idSeller FROM your first choice 

    IF @Seller IS NOT NULL BEGIN 
    SELECT * FROM Seller WHERE idSeller = @idSeller 
    RETURN 
    END 

    SELECT TOP 1 @idSeller = idSeller FROM your second choice 
    SELECT * FROM Seller WHERE idSeller = @idSeller 
    RETURN 
    END 

..and so one 
END

編輯：@Dasblinkenlight可能有它的權利，在SQL Server的查詢優化器可能會做這樣的事情在內部，你可以看看探查，看看這是什麼真正與發生聯盟。

來源

2014-03-07 13:43:40

這是要看的東西。有人對此有比較嗎？我之前想過要問，但我認爲我必須這樣做。 – rcdmk

什麼性能更好：UNION查詢和separete查詢的一堆？

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