inner joins and where

Hi all

I have been trying to do this for days and so decided to ask for some advice.

We have 4 tables and want to write a query for php that essentially checks
1) id from one table (a/) is in another(b) AND 2) id from one table (c) is not in (d)
3) the date from b is before now()

I get that I need to do an inner join on all 4 tables but not sure about the where and especially how to write the not part. I thought would be
user.userID=!cart.userID but it doesnt work


Please help

Thanks

Nicole

sorry number 1) should read
1) id from one table (a/) is in another(d)

Nicole