What formula do I need and where in Crystal Reports XI to get from A to B?

I have one table with 3 fields that I would like to suppress in a certain way.
I want to run a report that will show any member that did not use my
gym in the month of July,
so if the value in the Date In field = July, then do not show that person at all.  
A-original List                          B-What I want my report to show
Date In    Member ID    Member Name      Date In    Member ID    Member Name
4/1/06       1           Anthony         3/2/06       2          Bob
4/5/06                                   6/5/06
5/2/06                                   3/15/06      4          David
7/17/06                                  5/1/06
3/2/06       2            Bob
6/5/06
2/4/06       3            Cathy
2/5/06
7/5/06
3/15/06      4            David
5/1/06

as far as I am aware,  no version of CR or Business Objects supports NULL joins.

i.e.  Give me all the records in the left hand table where this is no
entry in the right hand table.  This has agravated me for about 5
years!!

Two things.

If this is the format of your data with multiple dates without the
supporting member ID then your data is not normalised correctly and
you should look seriously at what you are trying to do. :)

I would try to do something like the following:-

Create a variable field for the report (hidden of course) that  = 1 if
the month is the month you are looking for and zero if not.

Sum the variable in the group header / footer

Set the display property of the detail section to hidden based on a
formula that checks the sum total of the variable.

i dont have CR this machine so I can't work the formula for you, but
check the CR knowlege base at Crystal Decisions.

This will probably work for screen / print / web display but may not
work for exported report results.  Not sure whether they take into
account the hidden property.

good luck