Re: Wacky query plan, why?

On Fri, 25 Jul 2003, Maksim Likharev wrote:

> I have 2 queries, one is never returns, like explain shows 677195846.00
> cost
>     and another doing the same job works ( cost 6072.00 )
>
> I do not understand one thing, why query number one, generates so
> unbelievably
> screwed up plan?
>
> why it does not use index?
>
> query # 1:
> ------------------------------------------------------------------------
> ------
> explain update prod.t_results set expdate=e.termdate from
>     work.termdate e, prod.t_results r where e.docid=r.docid;

This is almost certainly not what you meant.  You haven't constrained
the update table (t_results) to the results of the from.  Adding t_results
r to the from joins an additional copy of the table (it's not an alias for
the update table).

Why not just
 update prod.tresults set expdate=e.termdate from work.termdate where
  e.docid=t_results.docid;
?