Why is there no "product()" aggregate function in SQL? [duplicate] - sql

Question

This question already has answers here:
is there a PRODUCT function like there is a SUM function in Oracle SQL?
(7 answers)
Closed 7 years ago.
When there are Sum(), min(), max(), avg(), count() functions, can someone help understand why there is no product() built-in function. And what will be the most efficient user-implementation of this aggregate function ?
Thanks,
Trinity

Answer 1

If you have exponential and log functions available, then:
PRODUCT(TheColumn) = EXP(SUM(LN(TheColumn)))

Answer 2

One can make a user-defined aggregate in SQL 2005 and up by using CLR. In Postgresql, you can do it in Postgres itself, likewise with Oracle

Answer 3

I'll focus on the question why it's not a standard function.
Aggregate function are basic statistical functions and product is not
Applied to common numerical data, the result will be in most cases out of range (overflow) so it is of little general use

Answer 4

It's probably left out because most people don't need it and it can be defined easily in most databases.
Solution for PostgreSQL:
CREATE OR REPLACE FUNCTION product_sfunc(state numeric, factor numeric)
RETURNS numeric AS $$
SELECT $1 * $2
$$ LANGUAGE sql;
CREATE AGGREGATE product (
sfunc = product_sfunc,
basetype = numeric,
stype = numeric,
initcond = '1'
);

Answer 5

You can simulate product() using cursors. If you let us know which database platform you're using, then we might be able to give you some sample code.

Answer 6

I can confirm that it is indeed rare to use a product() aggregate function, but I have a quite valid example, especially working with highly aggregated data that must be presented to users in a report.
It utilizes the exp(sum(ln( multiplyTheseColumnValues ))) "trick" as mentioned in another post and other internet sources.
The report (which should care about the display, and contain as least data calculation logic as possible, to provide better maintainability and flexibility) is basically displaying this data along with some graphics:
DESCR SUM
---------------------------------- ----------
money available in 2013 33233235.3
money spent in 2013 4253235.3
money bound to contracts in 2013 34333500
money spent 2013 in % of available 12
money bound 2013 in % of available 103
(In real life its a bit more complex and used in state budget scenarios.)
It aggregates quite some complex data found in the first 3 rows.
I do not want to calculate the percentage values of the following rows (4th and 5th) by:
doing it in the quite dumb (as it should be) report (which just takes any number of such rows with a descripiton descr and a number sum) with some fancy logic (using JasperReports, BIRT Reports or alike)
neither do I want to calculate the underlying data (money available, money spent, money bound) multiple times (since these are quite expensive operations) just to calculate the percentage values
So I used another trick involving the use of the product()-functionality.
(If somebody does know of a better way to achive this considering the above mentioned restrictions, I would be happy to know :-) )
The whole simplified example is available as one executable SQL below.
Maybe it could help convice some Oracle guys that this functionality is not as rare, or not worth providing, as it may seem at first thoughts.
with
-- we have some 10g database without pivot/unpivot functionality
-- what is interesting for various summary reports
sum_data_meta as (
select 'MA' as sum_id, 'money available in 2013' as descr, 1 as agg_lvl from dual
union all select 'MS', 'money spent in 2013', 1 from dual
union all select 'MB', 'money bound to contracts in 2013', 1 from dual
union all select 'MSP', 'money spent 2013 in % of available', 2 from dual
union all select 'MBP', 'money bound 2013 in % of available', 2 from dual
)
/* select * from sum_data_meta
SUM_ID DESCR AGG_LVL
------ ---------------------------------- -------
MA money available in 2013 1
MS money spent in 2013 1
MB money bound to contracts in 2013 1
MSP money spent 2013 in % of available 2
MBP money bound 2013 in % of available 2
*/
-- 1st level of aggregation with the base data (the data actually comes from complex (sub)SQLs)
,sum_data_lvl1_base as (
select 'MA' as sum_id, 33233235.3 as sum from dual
union all select 'MS', 4253235.3 from dual
union all select 'MB', 34333500 from dual
)
/* select * from sum_data_lvl1_base
SUM_ID SUM
------ ----------
MA 33233235.3
MS 4253235.3
MB 34333500.0
*/
-- 1st level of aggregation with enhanced meta data infos
,sum_data_lvl1 as (
select
m.descr,
b.sum,
m.agg_lvl,
m.sum_id
from sum_data_meta m
left outer join sum_data_lvl1_base b on (b.sum_id=m.sum_id)
)
/* select * from sum_data_lvl1
DESCR SUM AGG_LVL SUM_ID
---------------------------------- ---------- ------- ------
money available in 2013 33233235.3 1 MA
money spent in 2013 4253235.3 1 MS
money bound to contracts in 2013 34333500.0 1 MB
money spent 2013 in % of available - 2 MSP
money bound 2013 in % of available - 2 MBP
*/
select
descr,
case
when agg_lvl < 2 then sum
when agg_lvl = 2 then -- our level where we have to calculate some things based on the previous level calculations < 2
case
when sum_id = 'MSP' then
-- we want to calculate MS/MA by tricky aggregating the product of
-- (MA row:) 1/33233235.3 * (MS:) 4253235.3/1 * (MB:) 1/1 * (MSP:) 1/1 * (MBP:) * 1/1
trunc( -- cut of fractions, e.g. 12.7981 => 12
exp(sum(ln( -- trick simulating product(...) as mentioned here: http://stackoverflow.com/a/404761/1915920
case when sum_id = 'MS' then sum else 1 end
/ case when sum_id = 'MA' then sum else 1 end
)) over ()) -- "over()" => look at all resulting rows like an aggregate function
* 100 -- % display style
)
when sum_id = 'MBP' then
-- we want to calculate MB/MA by tricky aggregating the product as shown above with MSP
trunc(
exp(sum(ln(
case when sum_id = 'MB' then sum else 1 end
/ case when sum_id = 'MA' then sum else 1 end
)) over ())
* 100
)
else -1 -- indicates problem
end
else null -- will be calculated in a further step later on
end as sum,
agg_lvl,
sum_id
from sum_data_lvl1
/*
DESCR SUM AGG_LVL SUM_ID
---------------------------------- ---------- ------- ------
money available in 2013 33233235.3 1 MA
money spent in 2013 4253235.3 1 MS
money bound to contracts in 2013 34333500 1 MB
money spent 2013 in % of available 12 2 MSP
money bound 2013 in % of available 103 2 MBP
*/

Answer 7

Since the Product is noting but the multiple of SUM, so in SQL they didnot introduce the Product aggregate function
For example: 6 * 4 can be acheived by
either adding 6, 4 times to itself like 6+6+6+6
or
adding 4, 6 times to itself like 4+4+4+4+4+4
thus giving the same result