On Wed, Jan 28, 2009 at 11:37 PM, Scott Marlowe <scott.marl...@gmail.com>wrote:
> On Thu, Jan 29, 2009 at 12:01 AM, Kevin Traster <ke...@mffais.com> wrote: > > 2 questions: > > > > 1) Different costs for same actions. Doing an explain on 2 nearly > identical > > queries both involving the same Index scan on same table has 2 widely > > different costs for same Index scan 303375872.86 vs. 12576.70 > > Pretty sure this is a FAQ by now. > > not in and except treat nulls differently. If you table has nullable > fields and nulls would break your query, then not in () is a bad > choice. Therefore, effort to optimize had been placed into except, > which is distinctly, symantically different from not in (). > > It seems like some shift in the pg community has happened where we're > suddenly getting a lot of folks who came from a database where not in > and except are treated the same, even though they most definitely do > not mean the same thing. >
