Different results for Date range

[zdtic03]

I have a query that counts records between 2 dates.
When I use
to_char(LAST_CN T_DATE_TIME,'YY YY/MM/DD') between
'2015/09/01' and
'2015/09/23'
result is 11405

When I use
LAST_CNT_DATE_T IME between
to_date('2015/09/01','YYYY/MM/DD') and
to_date('2015/09/23','YYYY/MM/DD')

result is 9389
I am more apt to use the first
sometimes the results are the same
Thanks

[Rabbit]

You're not accounting for the time.

to_date('2015/09/01','YYYY/MM/DD') and to_date('2015/09/23','YYYY/MM/DD')
have a time value of midnight, 00:00:00.000000 . LAST_CNT_DATE_T IME with a time value after midnight on 9/23 don't get counted because it's outside the range you're looking for.

You should truncate the time portion of LAST_CNT_DATE_T IME before trying to filter it on your date range.