Considering the execution plan for this query :
SQL_ID 1m5r644say02b, child number 0
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select * from hr.employees where department_id = 80 intersect select *
from hr.employees where first_name like 'A%'
Plan hash value: 1738366820
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| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers | OMem | 1Mem | Used-Mem |
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| 0 | SELECT STATEMENT | | 1 | | 4 |00:00:00.01 | 8 | | | |
| 1 | INTERSECTION | | 1 | | 4 |00:00:00.01 | 8 | | | |
| 2 | SORT UNIQUE | | 1 | 34 | 34 |00:00:00.01 | 6 | 6144 | 6144 | 6144 (0)|
|* 3 | TABLE ACCESS FULL | EMPLOYEES | 1 | 34 | 34 |00:00:00.01 | 6 | | | |
| 4 | SORT UNIQUE | | 1 | 11 | 10 |00:00:00.01 | 2 | 2048 | 2048 | 2048 (0)|
| 5 | TABLE ACCESS BY INDEX ROWID BATCHED| EMPLOYEES | 1 | 11 | 10 |00:00:00.01 | 2 | | | |
|* 6 | INDEX SKIP SCAN | EMP_NAME_IX | 1 | 11 | 10 |00:00:00.01 | 1 | | | |
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Predicate Information (identified by operation id):
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3 - filter("DEPARTMENT_ID"=80)
6 - access("FIRST_NAME" LIKE 'A%')
filter("FIRST_NAME" LIKE 'A%')
The execution plan has both access and filter predicates with the same '%A' predicate here on the EMP_NAME_IX index. But shouldn't the access predicate be enough here, as they both will filter the same rows? Why did it perform the additional filter predicate?