SQL: Conditionally join on a date table if value found - sql

Question

I want to return the columns found in a date dimension, if the values in my columns in a separate dimension are valid and match keys in the date dimension. But, I want to do this conditionally, checking first for attributeOne and whether or not a date key exists there that can map the date dimension, then checking attributeTwo, and so on.
How can I specify a join to the date dimension such that all possible columns that I want to check join if found (e.g., attributeOne, attributeTwo, attributeThree, etc) so I can conditionally report/return the date dimension columns for that match.
JOIN #date D on D.dateKey = d1.attributeOne;
Consider this probably far too contrived example:
drop table #date;
drop table #dim;
drop table #fact;
CREATE TABLE #date (dateKey int, dateVal varchar(25))
INSERT #date (dateKey, dateVal)
VALUES
(20000101, 'FY1')
,(20000102, 'FY2')
,(20000103, 'FY3')
,(20000104, 'FY4')
,(20000105, 'FY5')
CREATE TABLE #dim (dKey int, attributeOne int, attributeTwo int, attributeThree int)
INSERT #dim (dKey, attributeOne, attributeTwo, attributeThree)
VALUES
(1, 20000101, 20000102, NULL)
,(2, NULL, 20000104, 20000105)
,(3, 20000301, 20000501, 20000104)
,(4, NULL, 20000102, NULL)
CREATE TABLE #fact (fKey int, Naming varchar(25))
INSERT #fact (fKey, Naming)
VALUES
(1, 'ex1')
,(2, 'ex2')
,(3, 'ex3')
,(4, 'ex4')
-- how to
select
f.fKey as 'F Key',
CASE
WHEN d1.attributeOne = D.dateKey THEN D.dateVal
WHEN d1.attributeTwo = D.dateKey THEN D.dateVal
WHEN d1.attributeThree = D.dateKey THEN D.dateVal
ELSE '<missing>' END AS "attributeOne"
from #fact f
JOIN #dim d1 on f.fKey = d1.dKey
JOIN #date D on D.dateKey = d1.attributeOne;

Answer 1

Maybe something like joining on an IN with some conditional aggregation?
select fact.Naming
, MAX(CASE WHEN dim.attributeOne = dt.dateKey THEN dt.dateVal WHEN dim.attributeOne IS NOT NULL THEN '<missing>' ELSE '' END) AS attributeOne
, MAX(CASE WHEN dim.attributeTwo = dt.dateKey THEN dt.dateVal WHEN dim.attributeTwo IS NOT NULL THEN '<missing>' ELSE '' END) AS attributeTwo
, MAX(CASE WHEN dim.attributeThree = dt.dateKey THEN dt.dateVal WHEN dim.attributeThree IS NOT NULL THEN '<missing>' ELSE '' END) AS attributeThree
FROM #fact AS fact
LEFT JOIN #dim AS dim
ON dim.dKey = fact.fKey
LEFT JOIN #date AS dt
ON dt.dateKey IN (dim.attributeOne, dim.attributeTwo, dim.attributeThree)
GROUP BY fact.fKey, fact.Naming
ORDER BY fact.fKey
Naming | attributeOne | attributeTwo | attributeThree
:----- | :----------- | :----------- | :-------------
ex1 | FY1 | FY2 |
ex2 | | FY4 | FY5
ex3 | <missing> | <missing> | FY4
ex4 | | FY2 |
db<>fiddle here