oracle索引问题
select distinct ab.other_tuangou,
ab.other_seller
from am_log_xx_xxx ab
where ab.inout = 'IN'
and ab.we_seller = 141508165094900002
AND ab.log_datetime >=
to_date('2013-12-01', 'YYYY-MM-DD')
AND ab.log_datetime <
to_date('2015-12-01', 'YYYY-MM-DD') + 1
create index IDX_AB_xx on am_log_xx_xxx(INOUT, OTHER_SELLER, WE_TUANGOU, WE_SELLER, LOG_DATETIME);
先建了一个组合索引,但是组合索引里面没加OTHER_TUANGOU,所以查询出来1.2s左右
但是我把上句索引改成下面这条,在组合索引里面加了OTHER_TUANGOU,查询出来0.2s
create index IDX_AB_xx on am_log_xx_xxx(INOUT, OTHER_SELLER, WE_TUANGOU, OTHER_TUANGOU, WE_SELLER, LOG_DATETIME);
复合索引有两个重要原则需要把握: 前缀性和可选性,但是不知道加了OTHER_TUANGOU为什么会快这么多???
谁给解释下??