Shulou(Shulou.com)06/01 Report--

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.

1 access: directly obtain those data that meet the conditions, and discard other data that are not satisfied

2 filter: you already have some data, apply filter to the existing data and get the data that meets the filter.

Many blog forums have the following conclusions:

Access indicates that the value of this predicate condition will affect the access path of the data (table or index), while filter indicates that the value of the predicate condition does not affect the data access path, but only acts as a filter.

But this conclusion is vague and easily ambiguous. Many people think that oracle does not have the choice of access index path as soon as it shows filter, and must take a full table scan for data selection. Is that true?

You can simulate the following scenarios:

Create table test (aa int, bb int) as select rownum,rownum from dba_objects; (10w data volume)

Create index.... Create an index on aa

Select count (aa) from test where aa

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