You could use a CTE with ROW_NUMBER function:
WITH CTE AS( SELECT myTable.* , RN = ROW_NUMBER()OVER(PARTITION BY patientID ORDER BY ID) FROM myTable )SELECT * FROM CTEWHERE RN = 1
It sounds like you're looking for DISTINCT:
SELECT DISTINCT patientID FROM myTable
you can get the same "effect" with GROUP BY:
SELECT patientID FROM myTable GROUP BY patientID
The simple way would be to add LIMIT 1 to the end of your query. This will ensure only a single row is returned in the result set.