On 3/6/21 9:00 PM, David Fetter wrote: > On Sat, Mar 06, 2021 at 08:57:46PM +0100, Vik Fearing wrote: >> On 3/6/21 8:55 PM, David Fetter wrote: >>> On Wed, Mar 03, 2021 at 03:30:15PM +0100, Peter Eisentraut wrote: >>>> On 10.02.21 06:42, Kyotaro Horiguchi wrote: >>>>> We already had CREATE AGGREATE at the time, so BIT_XOR can be >>>>> thought as it falls into the same category with BIT_AND and >>>>> BIT_OR, that is, we may have BIT_XOR as an intrinsic aggregation? >>>> >>>> I think the use of BIT_XOR is quite separate from BIT_AND and >>>> BIT_OR. The latter give you an "all" or "any" result of the bits >>>> set. BIT_XOR will return 1 or true if an odd number of inputs are 1 >>>> or true, which isn't useful by itself. But it can be used as a >>>> checksum, so it seems pretty reasonable to me to add it. Perhaps >>>> the use case could be pointed out in the documentation. >>> >>> If this is the only use case, is there some way to refuse to execute >>> it if it doesn't contain an unambiguous ORDER BY, as illustrated >>> below? >>> >>> SELECT BIT_XOR(b ORDER BY a, c)... /* works */ >>> SELECT BIT_XOR(b) OVER (ORDER BY a, c)... /* works */ >>> SELECT BIT_XOR(b) FROM... /* errors out */ >> >> >> Why would such an error be necessary, or even desirable? > > Because there is no way to ensure that the results remain consistent > from one execution to the next without such a guarantee.
I think one of us is forgetting how XOR works. -- Vik Fearing
