Re: Re: [SQL] Difficult SQL Statement

I wrote:
> select ASMT_CODE, PASSED, TOTAL, PASSED::float4/TOTAL::float4
> from
> (select ASMT_CODE, count(*) as TOTAL from RESULTS
> group by ASMT_CODE) as tmp1
> natural join
> (select ASMT_CODE, count(*) as PASSED from RESULTS
> where STATUS='PASSED' group by ASMT_CODE) as tmp2

BTW, although this is a fine example of how to avoid using temp tables,
it's not such a great solution to the original problem. What happens
if there are no 'PASSED' entries at all for a given ASMT_CODE? You
probably won't want that ASMT_CODE to disappear from your report ---
but it will disappear in the join. We could fix this with a left join
and some hackery to deal with the resulting NULL values for PASSED,
but now things are getting ugly. Time to try something different:

select ASMT_CODE, PASSED, TOTAL, PASSED::float4/TOTAL::float4 as PCT
from
(select ASMT_CODE,
count(*) as TOTAL,
sum(CASE WHEN STATUS='PASSED' THEN 1 ELSE 0 END) as PASSED
from RESULTS group by ASMT_CODE) as tmp1

Here we use the sub-select only as a way of labeling the count() and
sum() results so that we don't have to write and compute them twice.
You could write it as a simple one-level SELECT if you didn't mind
that redundancy.

regards, tom lane