Merge Columns into One Column Oracle PL/SQL - oracle

Question

I have the following script and tables where upon running the script produces the output for LOG_ID, YEAR, WA.SUB_DIVISION, AI.SUB_DIVISION, EA.SUB_DIVISION, FI.SUB_DIVISION
Is it possible to Merge four columns into one column
WA.SUB_DIVISION, AI.SUB_DIVISION, EA.SUB_DIVISION, FI.SUB_DIVISION into SUB_DIVISION a single column
Not sure how to proceed.
I have created a sample sql fiddle
https://dbfiddle.uk/?rdbms=oracle_18&fiddle=3c4abb924462dcf5e5f8b0f91019b6b6
select distinct L.LOG_ID,
FC.LOG_YR as YEAR,
WA.SUB_DIVISION,
AI.SUB_DIVISION AS SUB_DIV,
EA.SUB_DIVISION AS SUB_DIV3,
FI.SUB_DIVISION AS SUB_DIV4
FROM FINAL_CALENDAR FC
JOIN LOG L
ON TO_DATE ( TO_CHAR (L.LOG_DATE, 'MM/DD/YYYY'), 'MM/DD/YYYY') = FC.CAL_DATE
LEFT OUTER JOIN LOG_WATER WA
ON WA.LOG_ID = L.LOG_ID
LEFT OUTER JOIN LOG_AIR AI
ON AI.LOG_ID = L.LOG_ID
LEFT OUTER JOIN LOG_EARTH EA
ON EA.LOG_ID = L.LOG_ID
LEFT OUTER JOIN LOG_FIRE FI
ON FI.LOG_ID = L.LOG_ID
Actual Output / ISSUE / Existing Output
LOG_ID YEAR SUB_DIVISION SUB_DIV SUB_DIV3 SUB_DIV4
990741 2020 NULL NULL NULL NULL
990742 2020 NULL NULL NULL NULL
991122 2020 NULL NULL NULL NULL
991123 2020 NULL NULL NULL NULL
994461 2020 NULL 4 NULL NULL
994468 2020 NULL 2 NULL NULL
994466 2020 NULL 2 NULL NULL
994480 2020 8 NULL NULL NULL
994479 2020 8 NULL NULL NULL
994476 2020 6 NULL NULL NULL
994478 2020 6 NULL NULL NULL
994440 2020 NULL NULL NULL NULL
994432 2020 NULL NULL NULL NULL
994450 2020 NULL NULL NULL NULL
994154 2020 NULL NULL NULL NULL
Required / Desired Output
LOG_ID YEAR SUB_DIVISION DISPLAY_NAME
990741 2020 NULL NULL
990742 2020 NULL NULL
991122 2020 NULL NULL
991123 2020 NULL NULL
994461 2020 4 Triangle
994468 2020 2 Circle
994466 2020 2 Circle
994480 2020 8 Rhombus
994479 2020 8 Rhombus
994476 2020 6 Dot
994478 2020 6 Dot
994440 2020 NULL NULL
994432 2020 NULL NULL
994450 2020 NULL NULL
994154 2020 NULL NULL
Table LOG;
LOG_ID, LOG_DATE,
990741, to_date('21-JAN-20','DD-MON-RR')
990742 21-JAN-20
991122 24-JAN-20
991123 25-JAN-20
994461 25-JAN-20
994468 25-JAN-20
994466 25-JAN-20
994480 25-JAN-20
994479 25-JAN-20
994476 25-JAN-20
994478 25-JAN-20
994440 25-JAN-20
994432 25-JAN-20
994450 25-JAN-20
994154 25-JAN-20
TABLE FINAL_CALENDAR;
CAL_DATE CAL_MONTH LOG_YR
21-JAN-20 1 2020
21-JAN-20 1 2020
24-JAN-20 1 2020
25-JAN-20 1 2020
25-JAN-20 1 2020
25-JAN-20 1 2020
25-JAN-20 1 2020
25-JAN-20 1 2020
25-JAN-20 1 2020
25-JAN-20 1 2020
25-JAN-20 1 2020
25-JAN-20 1 2020
25-JAN-20 1 2020
25-JAN-20 1 2020
25-JAN-20 1 2020
TABLE LOG_AIR;
ID LOG_ID SUB_DIVISION
134 994468 2
132 994461 4
133 994466 2
TABLE LOG_WATER;
ID LOG_ID SUB_DIVISION
9345 994480 8
9344 994479 8
9342 994476 6
9343 994478 6
TABLE LOG_EARTH;
ID LOG_ID SUB_DIVISION
0118 994440 null
0117 994432 null
TABLE LOG_FIRE;
ID LOG_ID SUB_DIVISION
706 994450 null
705 994154 null
TABLE Z_SUB_DIVISION_TYPE;
SUB_DIVISION DISPLAY_NAME
1 Parallelogram
2 Circle
3 Square
4 Triangle
5 Tangent
6 Dot
7 Line
8 Rhombus
9 Trapezium

Answer 1

If that's the final result you can merge last four columns assuming one column has value and rest are null(sub division columns)
SELECT log_id,
year,
CASE
WHEN sub_division IS NULL AND SUB_DIV3 IS NULL AND SUB_DIV4 IS NULL THEN sub_div
WHEN sub_division IS NULL AND SUB_DIV IS NULL AND SUB_DIV4 IS NULL THEN sub_div3
WHEN sub_division IS NULL AND SUB_DIV IS NULL AND SUB_DIV3 IS NULL THEN sub_div4
ELSE
sub_division
END as sub_division,
display_name
FROM (SELECT DISTINCT L.log_id,
FC.log_yr AS YEAR,
WA.sub_division,
AI.sub_division AS SUB_DIV,
EA.sub_division
AS SUB_DIV3,
FI.sub_division AS SUB_DIV4,
(SELECT display_name
FROM z_sub_division_type a
WHERE a.sub_division = WA.sub_division
OR a.sub_division = AI.sub_division
OR a.sub_division = EA.sub_division
OR a.sub_division = FI.sub_division
) AS DISPLAY_NAME
FROM final_calendar FC
join log L
ON To_date (To_char (L.log_date, 'MM/DD/YYYY'), 'MM/DD/YYYY') =
FC.cal_date
left outer join log_water WA
ON WA.log_id = L.log_id
left outer join log_air AI
ON AI.log_id = L.log_id
left outer join log_earth EA
ON EA.log_id = L.log_id
left outer join log_fire FI
ON FI.log_id = L.log_id)
Edit 1:-This sql works assuming atleast one column has value and rest are null
Edit 2:- You can replace case clause with coalesce
coalesce(sub_division,sub_div,sub_div3,sub_div4) as sub_division