Rick,

why don't you use like this:

...
if(param='U') then
begin
Select *
From atable
some_big_join
Where unit_use='U'
...
end
else
begin
Select *
From atable
some_big_join
Where unit_use <>'U'
...
end
...


OR

Select *
From atable
some_big_join
Where
(unit_use=:param and unit_use='U') or
(unit_use<>'U' and :param<>'U')


one more question..
what are you doing with a 'select *' in a stored procedure???


Regards.
Ali