Retrieve a table to tallied numbers, best way - plsql

Question

I have query that runs as part of a function which produces a one row table full of counts, and averages, and comma separated lists like this:
select
(select
count(*)
from vw_disp_details
where round = 2013
and rating = 1) applicants,
(select
count(*)
from vw_disp_details
where round = 2013
and rating = 1
and applied != 'yes') s_applicants,
(select
LISTAGG(discipline, ',')
WITHIN GROUP (ORDER BY discipline)
from (select discipline,
count(*) discipline_number
from vw_disp_details
where round = 2013
and rating = 1
group by discipline)) disciplines,
(select
LISTAGG(discipline_count, ',')
WITHIN GROUP (ORDER BY discipline)
from (select discipline,
count(*) discipline_count
from vw_disp_details
where round = 2013
and rating = 1
group by discipline)) disciplines_count,
(select
round(avg(util.getawardstocols(application_id,'1','AWARD_NAME')), 2)
from vw_disp_details
where round = 2013
and rating = 1) average_award_score,
(select
round(avg(age))
from vw_disp_details
where round = 2013
and rating = 1) average_age
from dual;
Except that instead of 6 main sub-queries there are 23.
This returns something like this (if it were a CSV):
applicants | s_applicants | disciplines | disciplines_count | average_award_score | average_age
107 | 67 | "speed,accuracy,strength" | 3 | 97 | 23
Now I am programmatically swapping out the "rating = 1" part of the where clauses for other expressions. They all work rather quickly except for the "rating = 1" one which takes about 90 seconds to run and that is because the rating column in the vw_disp_details view is itself compiled by a sub-query:
(SELECT score
FROM read r,
eval_criteria_lookup ecl
WHERE r.criteria_id = ecl.criteria_id
AND r.application_id = a.lgo_application_id
AND criteria_description = 'Overall Score'
AND type = 'ABC'
) reader_rank
So when the function runs this extra query seems to slow everything down dramatically.
My question is, is there a better (more efficient) way to run a query like this that is basically just a series of counts and averages, and how can I refactor to optimize the speed so that the rating = 1 query doesn't take 90 seconds to run.

Answer 1

You could choose to MATERIALIZE the vw_disp_details VIEW. That would pre-calculate the value of the rating column. There are various options for how up-to-date a materialized view is kept, you would probably want to use the ON COMMIT clause so that vw_disp_details is always correct.
Have a look at the official documentation and see if that would work for you.
http://docs.oracle.com/cd/B28359_01/server.111/b28286/statements_6002.htm

Answer 2

Do all most of your queries in only one. Instead of doing:
select
(select (count(*) from my_tab) as count_all,
(select avg(age) from my_tab) as avg_age,
(select avg(mypkg.get_award(application_id) from my_tab) as_avg-app_id
from dual;
Just do:
select count(*), avg(age),avg(mypkg.get_award(application_id)) from my_tab;
And then, maybe you can do some union all for the other results. But this step all by itself should help.

Answer 3

I was able to solve this issue by doing two things: creating a new view that displayed only the results I needed, which gave me marginal gains in speed, and in that view moving the where clause of the sub-query that caused the lag into the where clause of the view and tacking on the result of the sub-query as column in the view. This still returns the same results thanks to the fact that there are always going to be records in the table the sub-query accessed for each row of the view query.
SELECT
a.application_id,
util.getstatus (a.application_id) status,
(SELECT score
FROM applicant_read ar,
eval_criteria_lookup ecl
WHERE ar.criteria_id = ecl.criteria_id
AND ar.application_id = a.application_id
AND criteria_description = 'Overall Score' //THESE TWO FIELDS
AND type = 'ABC' //ARE CRITERIA_ID = 15
) score
as.test_total test_total
FROM application a,
applicant_scores as
WHERE a.application_id = as.application_id(+);
Became
SELECT
a.application_id,
util.getstatus (a.application_id) status,
ar.score,
as.test_total test_total
FROM application a,
applicant_scores as,
applicant_read ar
WHERE a.application_id = as.application_id(+)
AND ar.application_id = a.application_id(+)
AND ar.criteria_id = 15;