Bruce Momjian <bruce@momjian.us> writes:
> On Thu, Aug 9, 2018 at 01:11:05PM +0300, KES wrote:
>> Why surprising? It is
>> [documented](https://www.postgresql.org/docs/current/static/sql-create
>> table.html#sql-createtable-exclude):
>>> If all of the specified operators test for equality, this is
>>> equivalent to a UNIQUE constraint, although an ordinary unique
>>> constraint will be faster.
>> Thus the UNIQUE constraint is just particular case of exclusion
>> constraint, is not?
> Well, for me a UNIQUE constraint guarantees each discrete value is
> unique, while exclusion constraint says discrete or ranges or geometric
> types don't overlap. I realize equality is a special case of discrete,
> but having such cases be marked as UNIQUE seems too confusing.
I think the OP is reading "equivalent" literally, as meaning that
an EXCLUDE with operators that act like equality is treated as being
the same as UNIQUE for *every* purpose. We're not going there, IMO,
so probably we need to tweak the doc wording a little. Perhaps
writing "functionally equivalent" would be better? Or instead of
"is equivalent to", write "imposes the same restriction as"?
regards, tom lane