import pandas as pd

df = pd.DataFrame(dict(c1=["xxxx1", "xxxx1", "xxxx1", "xxxx2", "xxxx3"],
                       c2=["NY", "NY", "NY", "DT", "ET"],
                       c3=["n1", "n2", "n3", "n4", "n5"]))


print(df.groupby(["c1", "c2"])["c3"].apply(lambda x: ', '.join(x)))

SELECT model_id, LISTAGG(vin, ', ') WITHIN GROUP (ORDER BY vin) FROM vehicle
GROUP BY model_id;