Oracle enforces index execution

Differences between adding a comment and canceling a comment: F5 shows the effect, and the execution time is compared to the forced execution index example.

Select count (1) FROM (select * from vav_stbms_tb_act_source_2012 where cstart_time> = to_date ('2017/1 02:00:00 ', 'yyyy/mm/dd hh24: MI: ss ') and cstart_time <to_date ('2014/2 02:00:00 ', 'yyyy/mm/dd hh24: MI: ss') and creceivenetworkid = 2011/11 UNION select/* + index (using VAV_SOURCE_INDEX2) */* from vav_stbms_tb_act_source_2012 where creceivedate> = to_date ('2017/1 02:00:00 ', 'yyyy/mm/dd hh24: MI: ss ') and creceivedate <to_date ('2014/1/2 02:00:00 ', 'yyyy/mm/dd hh24: MI: ss') and creceivenetworkid = 2011/11)/* cbo * // * rbo */