On Mon, Oct 13, 2014 at 2:05 PM, <michael@aplaypowered.com> wrote:
> case when sum( column1 ) = 0
> then 0
> else round( sum( price
> * hours
> / column1 ), 2 )
> I would expect that the else part would never be evaluated.
> Documentation only describes that this happens for immediates.
I explained this behavior in the Stack Overflow answer, it is caused
by way aggregates are evaluated in a SELECT (or HAVING) clause.
Our documentation should be clearer about the fact that all aggregates
are evaluated strictly before their surrounding SELECT expressions,
the attached documentation patch adds a note about this to the
"general processing of SELECT" explanation.
I also created a section "Implementation Notes" in the "Conditional
Expressions" chapter to explain this behavior, since conditionals is
where this behavior is most visible.
This similarly affects the HAVING clause:
db=# select sum(1/i) from unnest(array[0])i having min(i)>0;
ERROR: division by zero
Regards,
Marti
