How to use a global temporary table in a function? - sql

Question

so I have a function that takes in 3 IN parameters (hour, date, code)
and returns a number.
My function code is below:
create or replace FUNCTION get_max_value (rhr NUMBER,
rdate VARCHAR2,
rcode VARCHAR2)
RETURN NUMBER
IS
rvalue_day NUMBER;
--
BEGIN
SELECT MAX (v.value)
INTO rvalue_day
FROM table v
JOIN rel_table_1 sv ON (v.value_id = sv.value_id)
JOIN look_up_table ff ON (sv.form_field_id = ff.form_field_id)
WHERE v.date = rdate
AND v.code = rcode
AND v.hr_num = rhr
AND (v.code = 'PASS' OR v.code IS NULL);
RETURN rvalue_day;
END;
Because of performance issues, I am trying to use a global temporary table that grabs the values (v.value) and the primary_identifier associated to it (value_Id). My code is below:
with table_c as
(
select value, value_id
from table where date = rdate
AND code = rcode
AND hr_num = rhr
)
select MAX (v.value)
FROM table_c v
JOIN rel_table_1 sv ON (v.value_id = sv.value_id)
JOIN look_up_table ON (sv.form_field_id = ff.form_field_id)
WHERE ff.code_desc = rcode;
Is there a way I can incorporate the above method into a function so that it can accept values for multiple parameters? I currently have a stored proc that is trying to derive a value by inserting 3 values into those 3 parameters...
Thanks in advance!

Answer 1

This is not an answer to your question "how can I optimize this function".
I'm going to show you that the very idea of using a function can be a reason of your performance problems - and I'am guessing that this is the case in your case.
Please look at the below very simple case:
create table ttest as
select * from all_objects
fetch first 10000 rows only;
create index ttest_ix on ttest(object_type);
create or replace function get_max(p_object_type varchar)
return number
is
ret_val number;
begin
select max(object_id) into ret_val
from ttest
where object_type = p_object_type;
return ret_val;
end;
/
create or replace view get_max_view as
select object_type, max(object_id) as max_id
from ttest
group by object_type
;
The view get_max_view is an equivalent of the function get_max, you can use both for example in this way in queries:
select object_id, object_type, get_max(object_type) as max_id
from ttest;
select object_id, object_type,
(select max_id from get_max_view x where x.object_type = t.object_type) as max_id
from ttest t;
And now please examine the case where both the above queries are run against 10000 records - to do so I nest both queries as subqueries, and caclulate a sum of all their results:
set timings on;
select sum(max_id)
from (
select object_id, object_type, get_max(object_type) as max_id
from ttest
);
SUM(MAX_ID)
-----------
214087478
Elapsed: 00:00:11.764
select sum(max_id)
from (
select object_id, object_type,
(select max_id from get_max_view x where x.object_type = t.object_type) as max_id
from ttest t
);
SUM(MAX_ID)
-----------
214087478
Elapsed: 00:00:00.011
Please examine the times - 11.76 seconds vs. 11 miliseconds.
This is over 1000 times faster - 100000% faster !!!
This is why I suggested you in the comment to replace this functin by the view, because this is the most probably cause of your performance issues, and trying to optimize this function is probably the wrong way.