Cannot use group by and over(partition by) in the same query? - sql

Question

I have a table myTable with 3 columns. col_1 is an INTEGER and the other 2 columns are DOUBLE. For example, col_1={1, 2}, col_2={0.1, 0.2, 0.3}. Each element in col_1 is composed of all the values of col_2 and col_2 has repeated values for each element in col_1. The 3rd column can have any value as shown below:
col_1 | col_2 | Value
----------------------
1 | 0.1 | 1.0
1 | 0.2 | 2.0
1 | 0.2 | 3.0
1 | 0.3 | 4.0
1 | 0.3 | 5.0
2 | 0.1 | 6.0
2 | 0.1 | 7.0
2 | 0.1 | 8.0
2 | 0.2 | 9.0
2 | 0.3 | 10.0
What I want is to use an aggregate-function SUM() on the Value column partition by col_1 and grouped by col_2. The Above table should look like this:
col_1 | col_2 | sum_value
----------------------
1 | 0.1 | 1.0
1 | 0.2 | 5.0
1 | 0.3 | 9.0
2 | 0.1 | 21.0
2 | 0.2 | 9.0
2 | 0.3 | 10.0
I tried the following SQL query:
SELECT col_1, col_2, sum(Value) over(partition by col_1) as sum_value
from myTable
GROUP BY col_1, col_2
But on DB2 v10.5 it gave the following error:
SQL0119N An expression starting with "Value" specified in a SELECT
clause, HAVING clause, or ORDER BY clause is not specified in the
GROUP BY clause or it is in a SELECT clause, HAVING clause, or ORDER
BY clause with a column function and no GROUP BY clause is specified.
Can you kindly point out what is wrong. I do not have much experience with SQL.
Thank you.

Answer 1

Yes, you can, but you should be consistent regarding the grouping levels.
That is, if your query is a GROUP BY query, then in an analytic function
you can only use "detail" columns from the "non-analytic" part of your selected
columns.
Thus, you can use either the GROUP BY columns or the non-analytic aggregates,
like this example:
select product_id, company,
sum(members) as No_of_Members,
sum(sum(members)) over(partition by company) as TotalMembership
From Product_Membership
Group by Product_ID, Company
Hope that helps
SELECT col_1, col_2, sum(Value) over(partition by col_1) as sum_value
-- also try changing "col_1" to "col_2" in OVER
from myTable
GROUP BY col_2,col_1

Answer 2

I found the solution.
I do not need to use OVER(PARTITION BY col_1) because it is already in the GROUP BY clause. Thus, the following query gives me the right answer:
SELECT col_1, col_2, sum(Value) as sum_value
from myTable GROUP BY col_1, col_2
since I am already grouping w.r.t col_1 and col_2.
Dave, thanks, I got the idea from your post.