Re: Query plan for NOT IN

well, as a rule of thumb - unless you can't think of a default value of column - don't use nulls. So using nulls as default 'idunno' - is a bad practice, but everybody's opinion on that differ.

But back on a subject, postgresql is very very poor performance wise with [NOT] IN () type of constructs. So if you can, avoid them, and learn to use joins.