I am not very experienced in SQL, so I need some help.  Alright, typically
when I create an update query, I do a select query and get my desired results
and then convert it over to an Update query; however, this time I have run
into a few problems.  I know it is simple, I just can't figure it out.  Below
is my select query:

SELECT MAIN.PostID, Count(MAIN.PostID) AS PostCount, MAIN.Title, First(MAIN.
PostDate) AS FirstOfPostDate, MAIN.PostNumber, MAIN.Post
FROM MAIN
GROUP BY MAIN.PostID, MAIN.Title, MAIN.PostNumber;

Basically, I have the following scenario:
ID     Title           Date        PostNumber           Post
1         string1     Date1             1                       Post1
1         string1     Date2             1                       Post2
2         string2     Date3             1                       Post3
2         string2     Date4             1                       Post4
3         string3     Date5             1                       Post5
3         string3     Date6             1                       Post6
3         string3     Date7             1                       Post7
...

I want it to look like this:
ID     Title           Date        PostNumber           Post         Expr:
Count    
1         string1     Date1             1                       Post1
2
2         string2     Date3             1                       Post3
2
3         string3     Date5             1                       Post5
3

And I want to assign the CountValue to the PostNumber.

ID     Title           Date        PostNumber           Post         Expr:
Count    
1         string1     Date1             2                       Post1
2
2         string2     Date3             2                       Post3
2
3         string3     Date5             3                       Post5
3