>Thanks Sergey,
>
>The puzzling part for me was how the primary Select statement gets a match to the subquery. While this probably isn't valid SQL, I would have expected something like this where we specify we are looking for HouseholdID in the subquery to match the HouseholdID in the main query.
>

>SELECT *
>  FROM Household 
>  WHERE ApplicantID = @PersonId  
>    OR HouseholdID = (SELECT HouseholdID FROM HouseholdMembers WHERE PersonId =  @PersonId)
>

>In that case where trying to specifically select HouseholdID from the subquery.
>
>I guess it is this part of the subquery that does that magic. WHERE HouseholdID = Household.HouseholdID AND PersonId = @PersonId
>
>Basically it works so I am happy, but just trying to figure out so I understand.
>Thanks a bunch, I think I am making sense of it now.
>Tim
>

What you wrote is essentially the same as EXISTS query. But EXISTS is just a better syntax and also it does not suffer from the NULL problem that IN query suffers.

In order to CONNECT outer and inner queries, you use this

select * from HouseHold H1
where exists (select 1 (you can put * with the same effect here)
from HouseholdMembers M where H1.HouseHoldID = M.HouseHoldID -- this is the connection between outer and inner
AND M.PersonID = @PersonID)