我有一个想要优化的查询。这是查询：
SELECT CONN.connNum, MIN(INTER.walkingDistanceMinutes) AS minimalWalkingDistance
FROM INTER
INNER JOIN CONN ON (INTER.IDConn_FK = CONN.IDConn)
GROUP BY INTER.IDConn_FK, CONN.connNum;
这些是解释计划结果：
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| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
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| 0 | SELECT STATEMENT | | 3 | 171 | 7 (15)| 00:00:01 |
| 1 | HASH GROUP BY | | 3 | 171 | 7 (15)| 00:00:01 |
| 2 | NESTED LOOPS | | 3 | 171 | 6 (0)| 00:00:01 |
| 3 | NESTED LOOPS | | 3 | 171 | 6 (0)| 00:00:01 |
| 4 | TABLE ACCESS FULL | INTER | 3 | 78 | 3 (0)| 00:00:01 |
|* 5 | INDEX UNIQUE SCAN | SYS_C002012172 | 1 | | 0 (0)| 00:00:01 |
| 6 | TABLE ACCESS BY INDEX ROWID| CONN | 1 | 31 | 1 (0)| 00:00:01 |
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我尝试过使用更具体的SELECT，但结果是一样的（类似于FROM (SELECT IDConn_FK, walkingDistanceMinutes FROM INTER) I等）。你能告诉我一个降低成本的方法吗？