Oracle SQL: Merging multiple columns into 1 with conditions - sql

Question

I am new to SQL and don't really have a lot of experience. I need help on this where I have Table A and I want to write a SQL query to generate the result. Any help would be greatly appreciated! Thanks!
Table A
Name
Capacity A
Capacity B
Capacity C
Plant 1
10
20
Plant 2
10
Result Table
Name
Type
Capacity
Plant 1
A,C
10,20
Plant 2
B
10
I know listagg function might be able to combine few columns into one, but is there anyway for me to generate the additional column 'Type' where its smart enough to know which column I am taking my value from? Preferably without creating any additional views/table.

Answer 1

Use NVL2 (or CASE) and concatenate the columns and trim any excess trailing commas:
SELECT Name,
RTRIM(
NVL2(CapacityA,'A,',NULL)
||NVL2(CapacityB,'B,',NULL)
||NVL2(CapacityC,'C',NULL),
','
) AS type,
RTRIM(
NVL2(CapacityA,CapacityA||',',NULL)
||NVL2(CapacityB,CapacityB||',',NULL)
||NVL2(CapacityC,CapacityC,NULL),
','
) AS capacity
FROM table_name;
Which, for the sample data:
CREATE TABLE table_name (name, capacitya, capacityb, capacityc) AS
SELECT 'Plant1', 10, NULL, 20 FROM DUAL UNION ALL
SELECT 'Plant2', NULL, 10, NULL FROM DUAL;
Outputs:
NAME
TYPE
CAPACITY
Plant1
A,C
10,20
Plant2
B
10
db<>fiddle here

Answer 2

Here's one option:
sample data in lines #1 - 4
temp CTE simply - conditionally - concatenates types and capacities
final query (line #17)
removes double separators (commas) (regexp)
removes superfluous leading/trailing commas (trim)
SQL> with test (name, capa, capb, capc) as
2 (select 'Plant1', 10, null, 20 from dual union all
3 select 'Plant2', null, 10, null from dual
4 ),
5 temp as
6 (select name,
7 --
8 case when capa is not null then 'A' end ||','||
9 case when capb is not null then 'B' end ||','||
10 case when capc is not null then 'C' end as type,
11 --
12 case when capa is not null then capa end ||','||
13 case when capb is not null then capb end ||','||
14 case when capc is not null then capc end as capacity
15 from test
16 )
17 select name,
18 trim(both ',' from regexp_replace(type , ',+', ',')) as type,
19 trim(both ',' from regexp_replace(capacity, ',+', ',')) as capacity
20 from temp;
NAME TYPE CAPACITY
------ ---------- ----------
Plant1 A,C 10,20
Plant2 B 10
SQL>