DB interaction SQL

I am working on a JDBC program for which I am writing a query, now I know its not a SQL forum but I am hoping that somebody would be kind enough to put in a word or two.

Now when I run the following query

SELECT Count(*)

FROM ptedb.mon m, epay_msg.status st

WHERE to_char(m.pDATE,'DD-Mon-YY') >=to_char(st.tDATE,'DD-Mon-YY')

AND m.tdate > SYSDATE-7

however whn I run

SELECT Count(*)

FROM ptedb.mon m, epay_msg.status st

WHERE to_char(m.pDATE,'DD-Mon-YY') >=to_char(st.tDATE,'DD-Mon-YY')

it returns 7 results

and when I run

SELECT Count(*)

FROM ptedb.mon m, epay_msg.status st

WHERE m.tdate > SYSDATE-7

this also returns some results. So considering that I should get some no with the first query as well. Its really confusing me please advise.

[965 byte] By [LisaMa] at [2007-11-26 17:51:14]