如果是子查询,会变成表连接
SQL> select * from dual where dummy in(select dummy from dual);
D
-
X
执行计划
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Plan hash value: 1311262134
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| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 4 | 4 (0)| 00:00:01 |
| 1 | NESTED LOOPS SEMI | | 1 | 4 | 4 (0)| 00:00:01 |
| 2 | TABLE ACCESS FULL | DUAL | 1 | 2 | 2 (0)| 00:00:01 |
|* 3 | VIEW | VW_NSO_1 | 1 | 2 | 2 (0)| 00:00:01 |
| 4 | TABLE ACCESS FULL| DUAL | 1 | 2 | 2 (0)| 00:00:01 |
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Predicate Information (identified by operation id):
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3 - filter("DUMMY"="DUMMY")