Aggregating several columns in oracle sql - oracle

Question

Having a difficult time phrasing this question. Let me know if there's a better title.
I have a query that produces data like this:
+----------+----------+----------+----------+----------+
| KEY | FEB_GRP1 | JAN_GRP1 | FEB_GRP2 | JAN_GRP2 |
+----------+----------+----------+----------+----------+
| 50840992 | 1 | 1 | 0 | 0 |
| 50840921 | 0 | 1 | 1 | 0 |
| 50848995 | 0 | 0 | 0 | 0 |
+----------+----------+----------+----------+----------+
Alternatively, I can produce data like this:
+----------+------+------+
| KEY | JAN | FEB |
+----------+------+------+
| 50840992 | <50 | ~<50 |
| 50840921 | <50 | <50 |
| 50848995 | ~<50 | ~<50 |
| 50840885 | <50 | <50 |
+----------+------+------+
Where <50 should be counter as "group 1" and ~<50 should be counter as "group 2".
And I want it to be like this:
+-------+------+------+
| MONTH | GRP1 | GRP2 |
+-------+------+------+
| JAN | 2 | 0 |
| FEB | 1 | 1 |
+-------+------+------+
I can already get JAN_GRP1_SUM just by summing JAN_GRP1, but I want that to just be a data point, not a column itself.
My query (generates the first diagram):
SELECT *
FROM (
SELECT KEY,
CASE WHEN "FEB-1-2016" = '<50' THEN 1 ELSE 0 END AS FEB_GRP1,
CASE WHEN "FEB-1-2016" != '<50' THEN 1 ELSE 0 END AS FEB_GRP2,
CASE WHEN "JAN-1-2016" = '<50' THEN 1 ELSE 0 END AS JAN_GRP1,
CASE WHEN "JAN-1-2016" != '<50' THEN 1 ELSE 0 END AS JAN_GRP2
FROM MY_TABLE);

Answer 1

Your data model doesn't make much sense, but from what you've shown you can do:
select 'JAN' as month,
count(case when "JAN-1-2016" = '<50' then 1 end) as grp1,
count(case when "JAN-1-2016" != '<50' then 1 end) as grp2
from my_table
union all
select 'FEB' as month,
count(case when "FEB-1-2016" = '<50' then 1 end) as grp1,
count(case when "FEB-1-2016" != '<50' then 1 end) as grp2
from my_table;
That doesn't scale well - if you have more months you need to add another union branch for each one.
If your query is based on a view or a previously calculated summary then it will probably be much easier to go back to the original data.
If you are stuck with this then another possible approach, which might be more manageable if you actually have more than two months to look at, could be to unpivot the data:
select *
from my_table
unpivot(value for month in ("JAN-1-2016" as date '2016-01-01',
"FEB-1-2016" as date '2016-02-01') --, etc. for other months
);
and then aggregate that:
select to_char(month, 'MON', 'NLS_DATE_LANGUAGE=ENGLISH') as month,
count(case when value = '<50' then 1 end) as grp1,
count(case when value != '<50' then 1 end) as grp2
from (
select *
from my_table
unpivot(value for month in ("JAN-1-2016" as date '2016-01-01',
"FEB-1-2016" as date '2016-02-01') --, etc. for other months
)
)
group by month;
Still not pretty and Oracle is doing pretty much the same thing under the hood I think, but fewer case expressions to create and maintain - the drudge part is the unpivot pairs. You might need to include the year in the `'month' field, depending on the range of data you have.