Question

请建议我更好的代码

方法（A）

        MERGE /*+ Idx_Mrx_Strategy */INTO stgMurex m
        USING
        (
            SELECT  m.RowId  AS mRowId
            FROM    stgMurex m
            INNER JOIN LovDF_EMIR t
            ON      m.Strategy = t.Strategy
            WHERE   t.NonDF = 'Y'

        ) l
        ON (m.RowId = l.mRowId)
        WHEN MATCHED THEN
            UPDATE SET
                m.DF = 'N'
        WHERE   m.DF IS NULL
        ;

Rows    Plan
199448  MERGE STATEMENT  
     MERGE  STGMUREX
      VIEW  
199448     HASH JOIN  
199448      HASH JOIN  
130      TABLE ACCESS FULL LOVDF_EMIR
576864       TABLE ACCESS FULL STGMUREX
1426340     TABLE ACCESS FULL STGMUREX

方法（B）

        MERGE INTO stgMurex m
        USING
        (
            SELECT  t.Strategy 
            FROM    LovDF_EMIR t
            WHERE   t.NonDF = 'Y'
        ) l
        ON (m.Strategy = l.Strategy)
        WHEN MATCHED THEN
            UPDATE SET
                m.DF = 'N'
        WHERE m.DF IS NULL 
        ;

Rows    Plan
199448  MERGE STATEMENT  
     MERGE  STGMUREX
      VIEW  
199448     HASH JOIN  
130     TABLE ACCESS FULL LOVDF_EMIR
576864      TABLE ACCESS FULL STGMUREX

我可以说方法B最好吗？

Answer 1

我想（假设＆＃34;从驾驶表返回的成功行的百分比很小＆＃34;这可能是由＆＃34; t.NonDF =＆＃39; Y＆＃39;＆＃34引起的;）与join的合并效率更高：

UPDATE stgMurex m
SET m.DF    = 'N'
WHERE m.DF IS NULL
AND EXISTS
(SELECT 1 FROM LovDF_EMIR t WHERE t.NonDF = 'Y' AND m.Strategy = t.Strategy
);

这里有很好的解释：http://www.toadworld.com/platforms/oracle/w/wiki/4778.table-joins-versus-exists.aspx

哪种方法比较好？按rowid或列映射

1 个答案: