| 2 | UNION-ALL | | | | | |
|* 3 | TABLE ACCESS BY INDEX ROWID| a | 1 | 15 | 4 (0)| 00:00:01 |
|* 4 | INDEX RANGE SCAN | idx_a_pro | 3 | | 3 (0)| 00:00:01 |
|* 5 | TABLE ACCESS BY INDEX ROWID| a | 1 | 15 | 3 (0)| 00:00:01 |
| 6 | NESTED LOOPS | | 5 | 135 | 10 (10)| 00:00:01 |
| 7 | SORT UNIQUE | | 5 | 60 | 2 (0)| 00:00:01 |
|* 8 | INDEX RANGE SCAN | idx_b_un_pro_sub | 5 | 60 | 2 (0)| 00:00:01 |
|* 9 | INDEX RANGE SCAN | idx_a_pro | 3 | | 2 (0)| 00:00:01 |
--------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
3 - filter("attr"=TO_NUMBER(:A))
4 - access("pro"=TO_NUMBER(:B))
5 - filter("attr"=TO_NUMBER(:A))
8 - access("HPS"."pro"=TO_NUMBER(:C))
9 - access("T"."pro"="HPS"."SUB_pro")
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
24 consistent gets
0 physical reads
0 redo size
589 bytes sent via SQL*Net to client
487 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
2 sorts (memory)
0 sorts (disk)
1 rows processed
访问表a时选择了pro上的索引，虽然增加了一次访问次数，但是逻辑读却下降到了24.