union all 和 or 效率问题

Question

网上都说union all效率比or快，可是实际使用过程中发现or比union all快，sql语句如下，使用or查询耗时1s多，union all耗时2s多，表数据大概有8千万左右，是按天分区的。
union all 的sql语句1：
select * from t_m_train_record t where t.stunum='5111786145333504' and t.traintime between to_date('20180710122954','yyyymmddhh24miss') and to_date('20180710153940','yyyymmddhh24miss') union all select * from t_m_train_record t where t.stunum='5111786145333504' and t.traintime between to_date('20180711141455','yyyymmddhh24miss') and to_date('20180711161920','yyyymmddhh24miss');

or 的sql语句2：
select * from t_m_train_record t where t.stunum='5111786145333504' and t.traintime between to_date('20180710122954','yyyymmddhh24miss') and to_date('20180710153940','yyyymmddhh24miss') union all select * from t_m_train_record t where t.stunum='5111786145333504' and t.traintime between to_date('20180711141455','yyyymmddhh24miss') and to_date('20180711161920','yyyymmddhh24miss');

Answer 1

不考虑走索引优化之类的。从理论上or是要快一点，因为or只扫描一遍表， union要两次。 但是如果考虑索引的话union all可以比or要快
这个要看具体执行计划和表数据的分布情况