Oracle 执行计划中access 和 filter的区别

Oracle 执行计划中access 和 filter的区别

access就把数据从磁盘读到内存里都是业务所需要的数据（一般通过索引），
filter就把数据从磁盘读到内存后，还要去掉不符合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，比如全表扫描）

举个例子：
select * from king where id=1;(id字段上有索引时候，oracle)
执行计划：
--------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------------------
| 0 | SELECt STATEMENT | | 1 | 25 | 4 (0)| 00:00:01 |
| 1 | TABLE ACCESS BY INDEX ROWID| KING | 1 | 25 | 4 (0)| 00:00:01 |
|* 2 | INDEX RANGE SCAN | IDX_ID | 1 | | 3 (0)| 00:00:01 |
--------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

2 - access("ID"=1)

-----------此时就是access
-------------------------------------------------------------------------------------
如果id上没有索引：
select * from king where id=1;
执行计划：

--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 25 | 25233 (2)| 00:05:03 |
|* 1 | TABLE ACCESS FULL| KING | 1 | 25 | 25233 (2)| 00:05:03 |
--------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

1 - filter("ID"=1)

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