>Hi everybody,
>
>I have the following criteria on my form:
>

>Quotes Generated for Manufacturer [         ]            Model         [              ]
>    Exclude Customers who have purchased
>    Exclude Customers who haven't purchased
> Model year from [  ] through [  ]

>
>I'm trying to translate this into where condition.
>
>Exclude customers who have purchased is clear enough:
>

>where not exists (select 1 from myTable where Make = [] and Model = [] and Model year between [] and [])
>

>But how should I translate the second possibility - Exclude Customers who haven't purchased?
>
>Thanks in advance.

When I have a situation like that, I take a sheet of paper + a pencil and move away from the keyboard

When I was a student, I was taught something like algebra of sets

let C be the set of customers
let A be the set of customers who purchased
let B be the set of customers who did not purchase

It is clear that C = A + B ( where + stands for the union)

A would translate to something like [where exists(..a purchase..)]
B would translate to [where not exists(.. a purchase.)

excluding A = not A becomes [ not exists()]
excluding B = not B becomes [ not not exists()] or simply [exists()]

Excluding both A and B becomes the empty set or [ where false ]


Might be simpler to understand if you were asking
- include Customers who have purchased
- include Customers who haven't purchased

then including both of them becomes [ where ( A or B )]
Since we know that C = A + B, it becomes [ where true ] (or no condition at all )



In addition: A equals not B and B equals not A - since A + B = C


Update
There's also something like boolean algebra - the exclamation mark stands for not
see : http://en.wikipedia.org/wiki/De_Morgan%27s_laws

!( a and b) = !a or !b
!( a or b ) = !a and !b

excluding both a and b
!a and !b = !(a or b)

since
(1)  a = !b
(2)  b = !a
(3)  c = a + b

excluding both a and b
!a and !b = ( !a and !!a) = !(a or !a) = !(a or b) = !(c) = nothing