表结构几乎一样，数据一样，同样的查询，一个走索引，一个不走索引，是啥原因

走索引的执行计划:

 Plan Hash Value : 2020907732 ------------------------------------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost | Time | -------------------------------------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 10 | 250 | 66 | 00:00:01 | | * 1 | VIEW | | 10 | 250 | 66 | 00:00:01 | | * 2 | COUNT STOPKEY | | | | | | | 3 | VIEW | | 11 | 132 | 66 | 00:00:01 | | 4 | NESTED LOOPS OUTER | | 11 | 990 | 66 | 00:00:01 | | 5 | NESTED LOOPS OUTER | | 11 | 748 | 44 | 00:00:01 | | 6 | NESTED LOOPS | | 11 | 506 | 22 | 00:00:01 | | * 7 | TABLE ACCESS BY INDEX ROWID | T_PAY | 519661 | 12471864 | 10 | 00:00:01 | | 8 | INDEX FULL SCAN DESCENDING | IDX_PAY_MAIN_ID | 12 | | 3 | 00:00:01 | | * 9 | INDEX UNIQUE SCAN | PK_MAIN_ID | 1 | 22 | 1 | 00:00:01 | | * 10 | INDEX RANGE SCAN | IDX_SUB_MAIN_ID | 1 | 22 | 2 | 00:00:01 | | * 11 | INDEX RANGE SCAN | IDX_ADDR_MAIN_ID | 1 | 22 | 2 | 00:00:01 | -------------------------------------------------------------------------------------------------------------------- Predicate Information (identified by operation id): ------------------------------------------ * 1 - filter("T"."RN">=1) * 2 - filter(ROWNUM<=10) * 7 - filter("PAY"."TYPE"='1') * 9 - access("TMAIN"."ID"="PAY"."MAIN_ID") * 10 - access("TMAIN"."ID"="TSUB"."MAIN_ID"(+)) * 11 - access("TMAIN"."ID"="ADDR"."MAIN_ID"(+)) 

不走索引的执行计划:

 Plan Hash Value : 4219115835 ---------------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost | Time | ---------------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 10 | 250 | 24 | 00:00:01 | | * 1 | VIEW | | 10 | 250 | 24 | 00:00:01 | | * 2 | COUNT STOPKEY | | | | | | | * 3 | HASH JOIN | | 11 | 990 | 24 | 00:00:01 | | * 4 | HASH JOIN OUTER | | 97 | 6402 | 18 | 00:00:01 | | * 5 | HASH JOIN OUTER | | 97 | 4268 | 12 | 00:00:01 | | 6 | PARTITION RANGE ALL | | 97 | 2134 | 6 | 00:00:01 | | 7 | TABLE ACCESS FULL | T_MAIN_HIS | 97 | 2134 | 6 | 00:00:01 | | 8 | PARTITION RANGE ALL | | 91 | 2002 | 6 | 00:00:01 | | 9 | TABLE ACCESS FULL | T_ADDR_HIS | 91 | 2002 | 6 | 00:00:01 | | 10 | PARTITION RANGE ALL | | 97 | 2134 | 6 | 00:00:01 | | 11 | TABLE ACCESS FULL | T_SUB_HIS | 97 | 2134 | 6 | 00:00:01 | | 12 | PARTITION RANGE ALL | | 89 | 2136 | 6 | 00:00:01 | | * 13 | TABLE ACCESS FULL | T_PAY_HIS | 89 | 2136 | 6 | 00:00:01 | ---------------------------------------------------------------------------------------------- Predicate Information (identified by operation id): ------------------------------------------ * 1 - filter("T"."RN">=1) * 2 - filter(ROWNUM<=10) * 3 - access("TMAIN"."ID"="PAY"."MAIN_ID") * 4 - access("TMAIN"."ID"="TSUB"."MAIN_ID"(+)) * 5 - access("TMAIN"."ID"="ADDR"."MAIN_ID"(+)) * 13 - filter("PAY"."TYPE"='1') 

两个查询所使用的表，除了表名后者带 HIS 外，后者都是建了分区的，不过查询条件没用到分区列，索引是完全一样的，查询时都是直接查全表的 结果后者查询时间是前者的 5-6 倍

为啥后者会全表扫描呢

PS：数据库是 ORACLE