優化這個UPDATE語句不使用遊標

FOR v2 AS 
    c2 CURSOR FOR 
     SELECT he.MyPrimary, he.SomeCode, he.SomeName, pe.MyPrimary 
     FROM SomeTable he 
      INNER JOIN AnotherTable pe 
       ON (he.ColOne = pe.FooOne 
        AND he.ColTwo = pe.ColTwo 
        AND he.ColThree = pe.FooOne 
        AND he.SomeCode = pe.SomeCode) 
     WHERE he.relevancy = 1 AND he.ColThree = '2011-01-05' AND he.ColFive = 9 
DO 
    UPDATE AnotherTable SET match = he.MyPrimary, FooTwo = he.SomeCode, SomeName = he.SomeName WHERE MyPrimary = pe.MyPrimary; 

END FOR;

我上面的代碼，我試圖做到這一點，而無需使用遊標，但我不知道該怎麼辦的UPDATE聲明與INNER JOIN。基本上，我想要做的就是連接兩個表SomeTable和AnotherTable然後基於一些列的值從SomeTable，值複製到類似列AnotherTable。我正在使用DB2。優化這個UPDATE語句不使用遊標

編輯：我只是在尋找到這一點：INNER JOIN in UPDATE sql for DB2

它將使意義做這樣的事情，而不是：

UPDATE 
    SomeTable pe 
SET 
    match = (SELECT he.MyPrimary FROM SomeTable he WHERE he.ColOne = pe.FooOne 
          AND he.ColTwo = pe.ColTwo 
          AND he.ColThree = pe.FooOne 
          AND he.SomeCode = pe.SomeCode), 

    FooTwo = (SELECT he.SomeCode FROM SomeTable he WHERE he.ColOne = pe.FooOne 
          AND he.ColTwo = pe.ColTwo 
          AND he.ColThree = pe.FooOne 
          AND he.SomeCode = pe.SomeCode) 
WHERE 
    he.relevancy = 1 AND he.ColThree = '2011-01-05' AND he.ColFive = 9

來源

2011-05-06 Connection

由於你的鏈接所提到的，ISO/ANSI標準不允許在子查詢中使用Update語句之外的聯接。因此，你必須要麼做多的更新語句，或使每個列的子查詢。

Update AnotherTable 
Set match = (
       Select he.MyPrimary 
       From SomeTable he 
       Where he.ColOne = AnotherTable.FooOne 
        And he.ColTwo = AnotherTable.ColTwo 
        And he.ColThree = AnotherTable.FooOne 
        And he.SomeCode = AnotherTable.SomeCode 
        And he.relevancy = 1 
        And he.ColThree = '2011-01-05' 
        And he.ColFive = 9 
       ) 
    , FooTwo = (
       Select he.SomeCode 
       From SomeTable he 
       Where he.ColOne = AnotherTable.FooOne 
        And he.ColTwo = AnotherTable.ColTwo 
        And he.ColThree = AnotherTable.FooOne 
        And he.SomeCode = AnotherTable.SomeCode 
        And he.relevancy = 1 
        And he.ColThree = '2011-01-05' 
        And he.ColFive = 9 
       ) 
    , SomeName = (
        Select he.SomeName 
        From SomeTable he 
        Where he.ColOne = AnotherTable.FooOne 
         And he.ColTwo = AnotherTable.ColTwo 
         And he.ColThree = AnotherTable.FooOne 
         And he.SomeCode = AnotherTable.SomeCode 
         And he.relevancy = 1 
         And he.ColThree = '2011-01-05' 
         And he.ColFive = 9 
        ) 
Where Exists (
       Select 1 
       From SomeTable he 
       Where he.ColOne = AnotherTable.FooOne 
        And he.ColTwo = AnotherTable.ColTwo 
        And he.ColThree = AnotherTable.FooOne 
        And he.SomeCode = AnotherTable.SomeCode 
        And he.relevancy = 1 
        And he.ColThree = '2011-01-05' 
        And he.ColFive = 9 
       )

來源

2011-05-06 22:14:29 Thomas

我真的只是關心性能。這會比使用遊標的原始遊戲快嗎？ – Connection 2011-05-06 22:27:00

@SQLizer - 你將不得不測試它知道。查詢引擎可能會明智地意識到你正在試圖執行三個相同的子查詢。如果不是，另一個解決方案是三個更新查詢。這兩種解決方案之一應該比光標更快。 – Thomas 2011-05-06 22:51:31

貌似是因爲事情的方式設置在這裏，光標實際上比其他兩種解決方案快（分鐘）。所以現在看來，改變它沒有意義。 – Connection 2011-05-06 23:59:19

有一個更好的方法來做到這一點;

UPDATE SomeTable pe SET (match, FooTwo, SomeName) = (SELECT he.MyPrimary, he.SomeCode, he.SomeName 
                FROM AnotherTable he 
                WHERE he.ColOne = pe.FooOne 
                AND he.ColTwo = pe.ColTwo 
                AND he.ColThree = pe.FooOne 
                AND he.SomeCode = pe.SomeCode) 
WHERE he.relevancy = 1 
AND he.ColThree = '2011-01-05' 
AND he.ColFive = 9

這工作得很好，DB2的iSeries的版本。
如果你需要擔心NULL行，不要忘記你的存在子句：

AND EXISTS (SELECT '1' 
      FROM AnotherTable he 
      WHERE he.ColOne = pe.FooOne 
      AND he.ColTwo = pe.ColTwo 
      AND he.ColThree = pr.FooOne 
      AND he.SomeCode = pe.SomeCode)

加入，現有的WHERE條款後，在主UPDATE聲明。

來源

2011-06-23 21:50:42

優化這個UPDATE語句不使用遊標

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