Siddharth Jain <siddhsql(at)gmail(dot)com> writes:
> I think the two are equivalent. If not, could you please explain why?
Well, they're formally equivalent if you require there to be only one
X value per partition (ie, PARTITION BY LIST with only one listed value
per partition); if there's more, they're not the same thing.
Neither one guarantees that Y is globally unique. We have no mechanism
for enforcing uniqueness across partitions except for partition key
columns.
regards, tom lane