SQL - Sum of two values IN a Group By - sql

Question

I am trying to add two values or get sum of two values and show it under one Exchange Name. Data below:
Table
--------------------------------------------------
EXCHANGE NAME CODE TURNOVER TRADEDATE
PARIS PA 12 14-NOV-2019
SWISS SW 14 14-NOV-2019
NULL SA 2 14-NOV-2019
NULL MI 2 14-NOV-2019
MILAN MI_1 3 14-NOV-2019
My Query
----------------------------------------------------
SELECT CE.EXCHANGE_NAME, sum(CE.TURNOVER)
FROM CE
WHERE CE.tradedate = '14-NOV-2019'
GROUP BY CE.EXCHANGE_NAME
Result
-----------------------------------------------------
EXCHANGE NAME SUM
PARIS 12
SWISS 14
MILAN 3
What I would like to achieve is that the total for SWISS to be 16 and MILAN to be 5 as MI belongs to MILAN also. There are NULL Values for EXCHANGE NAME but they belong to a certain exchange (Swiss in this case and Milan) i.e. code SA belongs to SWISS and MI belongs to MILAN.
How can I accommodate this in my query for situation like SWISS and MILAN where I know which code belongs to EXCHANGE_NAME?
Many thanks

Answer 1

You can use COALESCE():
SELECT COALESCE(CE.EXCHANGE_NAME, 'SWISS') as EXCHANGE_NAME, SUM(CE.TURNOVER)
FROM CE
WHERE CE.tradedate = '14-NOV-2019'
GROUP BY COALESCE(CE.EXCHANGE_NAME, 'SWISS');
As a note: I like the use of DATE for date constants:
WHERE CE.tradedate = DATE '2019-11-14'
This allows the use of ISO standard date formatting.
EDIT:
Use a CASE expression:
SELECT (CASE WHEN CE.CODE = 'SA' THEN 'SWISS'
WHEN CE.CODE = 'MI_1' THEN 'MILAN'
ELSE CE.EXCHANGE_NAME
END) as EXCHANGE_NAME,
SUM(CE.TURNOVER)
FROM CE
WHERE CE.tradedate = DATE '2019-11-14'
GROUP BY (CASE WHEN CE.CODE = 'SA' THEN 'SWISS'
WHEN CE.CODE = 'MI_1' THEN 'MILAN'
ELSE CE.EXCHANGE_NAME
END);

Answer 2

To me, it looks like you have to create a mapping table which will map codes to exchange names:
SQL> create table exmap
2 (exchange_name varchar2(20),
3 code varchar2(10));
Table created.
SQL> insert into exmap
2 select 'PARIS', 'PA' from dual union all
3 select 'SWISS', 'SW' from dual union all
4 select 'SWISS', 'SA' from dual union all
5 select 'MILAN', 'MI' from dual union all
6 select 'MILAN', 'MI_1' from dual;
5 rows created.
SQL>
Now, with date in the CE table (the one you posted), you'd join those two tables:
SQL> select e.exchange_name,
2 sum(c.turnover) sum_turnover
3 from ce c join exmap e on e.code = c.code
4 group by e.exchange_name;
EXCHANGE_NAME SUM_TURNOVER
-------------------- ------------
PARIS 12
MILAN 5
SWISS 16
SQL>
Why such an approach? Because sooner or later you'll add something like this to the CE table (so PARIS will now be 20):
SQL> insert into ce values ('PARIS', 'PR', 8);
1 row created.
Now, if you choose to maintain the mapping within the code, you'll have to fix it everywhere, in all your stored procedures, reports, forms ... whatever uses that table, and add yet another CASE, e.g.
case when code in ('PA', 'PR') then 'PARIS'
... ^^^^
this
That might drive you mad. But, if you simply add it to the mapping table:
SQL> insert into exmap values ('PARIS', 'PR');
1 row created.
the "old" join query will work without any further action:
SQL> select e.exchange_name,
2 sum(c.turnover) sum_turnover
3 from ce c join exmap e on e.code = c.code
4 group by e.exchange_name;
EXCHANGE_NAME SUM_TURNOVER
-------------------- ------------
PARIS 20
MILAN 5
SWISS 16
SQL>

Answer 3

You can use COALESCE() to turn NULL values of EXCHANGE_NAME to 'SWISS':
SELECT COALESCE(CE.EXCHANGE_NAME, 'SWISS'), sum(CE.TURNOVER)
FROM CE
WHERE CE.tradedate = '14-NOV-2019'
GROUP BY COALESCE(CE.EXCHANGE_NAME, 'SWISS')
Edit: you can use handy Oracle function decode() to map the code to a default EXCHANGE_NAME:
SELECT
COALESCE(
CE.EXCHANGE_NAME,
DECODE(CE.CODE, 'SA', 'SWISS', 'MI_1', 'MILAN')
) EXCHANGE,
SUM(CE.TURNOVER)
FROM CE
WHERE CE.tradedate = '14-NOV-2019'
GROUP BY COALESCE(
CE.EXCHANGE_NAME,
DECODE(CE.CODE, 'SA', 'SWISS', 'MI_1', 'MILAN')
)
You can expand the DECODE() argument as needed for your use case.