Help with a WHERE on a LEFT JOIN SQL Query

Question

I\'m trying to construct a query that will include a column indicating whether or not a user has downloaded a document. I have a table called HasDownloaded with the followin

Answer 1

WHERE HasDownloaded.memberId IS NULL OR HasDownloaded.memberId = @memberId

would be the normal way to do that. Some would shorten it to:

WHERE COALESCE(HasDownloaded.memberId, @memberId) = @memberId

You can, as Matt B. shows, do it in your JOIN condition - but I think that's much more likely to confuse folks. If you don't understand WHY moving it to the JOIN clause works, then I'd strongly suggest staying away from it.