>Thanks Naomi.
>
>I read the blog post. A lot of replies to the post stated that they didn't agree, i.e. they thought the examples were 'mistakes' with poorly written sql - e.g. not using alias names to reference the columns. One person wrote that you should never have nulls in a key column. But who says the query has to be on a key? It seems to me that exists queries are just "better implemented". It seems like a deficiency in the query engine that it doesn't get the same result as an exists query. I would think that the "exists query" version given in the example would be functionally equivalent to the "in query"?
>
>Most of the replies though addressed issues with failing to use aliases, but no one gave an explanation as to why the exists query would work differently than the in query.
>
>I understand that "NULL + 1" = NULL, this makes sense, but the problem below doesn't, to me.
>
Most of the comments to that blog were written by people who didn't understand what that blog was saying.

There is another one which probably can explain the problem even better
http://wiki.lessthandot.com/index.php/Subquery_typo_with_using_in