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