SQL or Appian Expression to Achieve a Unique Select

I would do this on the DB side in a view:

SELECT
caseNum,
causeType
/* additional columns here */
FROM YOUR_TABLE a
WHERE a.causeType =
	CASE 
	WHEN (SELECT COUNT(*) FROM YOUR_TABLE b where b.caseNum=a.caseNum)=1 THEN a.causeType
	ELSE 'Primary'
END