请教执行计划里的 access和filter有什么区别？谢谢

earth2mars

Predicate Information (identified by operation id):
---------------------------------------------------
   2 - access("ORD"."DATE_PLACED">SYSDATE@!-1)
       filter(EXISTS (SELECT /*+ NO_UNNEST */ 0 FROM "PRODUCTS" "PRD"
          WHERE "PRD"."ID"=:B1 AND "PRD"."PRODUCT_GROUP"='CLASSICAL CD'))
   3 - filter("PRD"."PRODUCT_GROUP"='CLASSICAL CD')
   4 - access("PRD"."ID"=:B1)

Yong Huang

These two terms in the Predicate Information section indicate when the data source is reduced. Simply, access means only retrieve those records meeting the condition and ignore others. Filter means *after* you already got the data, go through them all and keep those meeting the condition and throw away the others.

If you find another way to describe the difference, share with us.

earth2mars

Yong Huang 发表于 2013-2-22 23:16
These two terms in the Predicate Information section indicate when the data source is reduced. Simpl ...

谢谢，没怎么看明白
是不是access是原始数据集的过滤，比如表？
filter是对中间结果的过滤？

gszoracle

access就把数据从磁盘读到内存里都是要的（一般通过索引），filter就把数据从磁盘读到内存后，还要扔掉不符合where条件的数据（即读取了很多不需要的数据，做了部分无用功）

younghuijun

Yong Huang的意思是：
These two terms in the Predicate Information section indicate when the data source is reduced. Simply, access means only retrieve those records meeting the condition and ignore others. Filter means *after* you already got the data, go through them all and keep those meeting the condition and throw away the others.

access: 直接获取那些满足条件的数据，抛弃其他不满足的数据
filter: 你已经有了一些数据，对这些已经有的数据应用filter，得到满足filter的数据。

sundog315

gszoracle 发表于 2013-2-24 14:23
access就把数据从磁盘读到内存里都是要的（一般通过索引），filter就把数据从磁盘读到内存后，还要扔掉不符 ...

gszoracle

sundog315 发表于 2013-3-11 09:34

谢谢版主鼓励