Re: left join + case - how is it processed?

>
>> I thought the where condition would cut down on the rows returned, then the
>> case statement would take effect to do the null check. It seems to be doing
>> it in reverse ??
> # explain analyze SELECT * from sq_vw_ast_perm where assetid='30748';
>
> It aperas to me that both of your statements have where clauses, but I
> believe where isn't that explicit.  I'm not sure the nature of your
> problem permits the query optimizer to eliminate rows at all, even
> with the where statement. "assetid" is probably not known when the
> query optimizer hits, because it is computed based on the nullness of
> the columns.  I'd assume that the optimizer *could* more easily
> optimize this if you had used coalesce rather than an ad-hoc method
> with CASE. My guess is you can exclude rows with WHERE if the the
> column used is an run-time computation involving an ad-hoc CASE.

No difference.

Full explain plan here:

http://explain-analyze.info/query_plans/2725-query-plan-1447

I can see it's doing the extra filter step at the start (4th line) which
is not present without the coalesce/case statement. I just don't
understand why it's being done at that stage.

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