如何在DB2 SQL中获取数据，限制返回的行数，并对一列的这些行求和？

Question

I have a simple query that returns some records:

select reference as ref, amount as amt
from my.table
where foo_ref like 'B%'
and foo_amount != 0.000
fetch first 12 rows only

What I would also like to do is to SUM the amt column for these 12 returned rows. I am a newbie to SQL so I am not sure how this is done. Any help is appreciated.

Answer 1

 select reference as ref, SUM(amount) as amt
 from my.table
 where foo_ref like 'B%'
 and foo_amount != 0.000
 group by reference
 fetch first 12 rows only

The SUM() adds the values in amount. I added a group by for the reference. The result will be a table that is a group of references with a sum of the amount.

Any time you use a SUM(), COUNT(), MAX(), MIN() - et cetera you also have to add a group by to fields that are not using these functions.

Answer 2

What version and release of DB2? There's some powerful OLAP functionality in current versions..

with tbl as (
   select reference as ref, amount as amt
   from my.table
   where foo_ref like 'B%'
     and foo_amount != 0.000
   order by ref
   fetch first 12 rows only )
select tbl.*, sum(amt) as tot_amt 
from tbl  
group by rollup ((ref,amt))

This will return 13 rows, with the 13th containing NULL for ref and amt while having the total for the 12 rows in tot_amt.