SQL> select rownum rn ,a.* from cnmir.ew_auctions a where rownum<50000;
Execution Plan
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Plan hash value: 721966694
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| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
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| 0 | SELECT STATEMENT | | 49999 | 4833K| 163 (2)| 00:00:02 |
|* 1 | COUNT STOPKEY | | | | | |
| 2 | TABLE ACCESS FULL| EW_AUCTIONS | 49999 | 4833K| 163 (2)| 00:00:02 |
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SQL> select * from cnmir.ew_auctions where issue_id<80;
Execution Plan
----------------------------------------------------------
Plan hash value: 518049957
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| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 99 | 1379 (2)| 00:00:17 |
|* 1 | TABLE ACCESS FULL| EW_AUCTIONS | 1 | 99 | 1379 (2)| 00:00:17 |
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可见COUNT STOPKEY 机制是只针对rownum而设定的!