How would you rewrite something like:
WHERE (COALESCE(b.quantity, 0) - COALESCE(b.deliveredsum, 0)) > 0;
I could write:
where case when b.quantity is null then 0 else b.quantity end - case when b.deliveredsum is null then 0 else b.deliveredsum end > 0
It is butt ugly, but is that the most efficient way to write it in 8.2.4?
Sim
Pavel Stehule wrote:
Hello
On 11/01/2008, Sim Zacks <sim@xxxxxxxxxxxxxx> wrote:
I changed it to "where f.commited is not true" and the query now takes 1 second as opposed to 60.
(much faster then the 3 seconds it took on 8.0.1, which could also be because of the coalesce there)
Is it considered better practice (or more efficient) to always use (x is not or x=value)
instead of coalesce? Or does it make more sense to turn on the option "transform_null_equals"?
You can use without coalesce() = some operator IS DISTINCT FROM ... .
Use coalesce only if you need some NON NULL value.
for you sample
where f.commited IS DISTINCT FROM true;
operator IS DISTINCT FROM is NULL insensitive
Regards
Pavel Stehule
Thank you much
Sim
I assume that the original query is something along the lines of
d left join f on (...) where coalesce(f.commited, false) = false
In the meantime, Sim would probably have better luck if he restructured
this particular clause in some other way, say
where f.commited is not true
or
where f.commited = false or f.commited is null
Note also that he really ought to move up to 8.2.6, as 8.2.4 is not
very sane about what IS NULL means for a left join's result.
regards, tom lane
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