Question

我有一个带子查询的oracle查询。子查询使用分析函数。如果将子查询更改为join，则执行时间会有明显改善。但在相同的其他类似查询中它仍然是相同的。在查看解释计划时，我能够发现显示出显着改进的子查询已更改为Oracle优化器自动加入。

当我搜索取消子查询的概念时，这基本上意味着将子查询转换为连接，它会在某些条件下提到，这种情况会发生。

https://blogs.oracle.com/optimizer/entry/optimizer_transformations_subquery_unesting_part_1

我不清楚的是解释计划，如何理解它多次执行

Query Synopsis:
 JOIN CONTRACT CONTRACT
  ON UWFILE.ID         =CONTRACT.UWFILE_ID
  AND CONTRACT.YEAR    = UWFILE.YEAR
  AND UWFILE.ORDER_NUM = CONTRACT.ORDER_NUM
  AND CONTRACT.ID     IN
    (SELECT ID
    FROM
      (SELECT ID,
        DENSE_RANK()over(partition BY CONTRACT.FACUL_NUM, CONTRACT.YEAR order by (CONTRACT.ENDOR_NUM) DESC) AS endor_rank
      FROM CONTRACT
      )
    WHERE endor_rank = 1
    )

Explain plan Synopsis:

Filter Predicates 
AND  CONTRACT.LAST_IN_FORCE=1                        

  EXISTS (SELECT 0 FROM (SELECT ID ID,DENSE_RANK() OVER ( PARTITION BY CONTRACT.FACUL_NUM,CONTRACT.YEAR ORDER BY INTERNAL_FUNCTION(CONTRACT.ENDOR_NUM) DESC  
VIEW  
   Filter Predicates  
   AND  

  ID=:B1  
  ENDOR_RANK=1 
 WINDOW  Filter Predicates DENSE_RANK() OVER ( PARTITION BY CONTRACT.FACUL_NUM,CONTRACT.YEAR ORDER BY INTERNAL_FUNCTION(CONTRACT.ENDOR_NUM) DESC )<=1

在分析函数的情况下，子查询不需要oracle

0 个答案: