Re: [19] Proposal: function markers to indicate collation/ctype sensitivity

On Tue, 2025-06-03 at 20:22 -0700, Jeff Davis wrote:
> EQUALITY marker: indicates that the function or index AM depends on
> CollOid for the equality semantics of the input expression. Examples:
> texteq(), btree AM, hash AM. (Note: EQUALITY is only important for
> non-
> deterministic collations and we might want to omit it if too many
> functions qualify, but it helps illustrate the rest of the proposal
> so
> I will leave it in for now.)

I had trouble contriving a case where tracking EQUALITY as a separate
marker would be practically useful. When we allow non-deterministic
collations at the database level in the future, it might be useful in a
case like:

    CREATE TABLE r(t TEXT, CHECK(length(t) <= 10));

because length() doesn't care about equality, so it would have no
dependency on the database collation even if it were, for example,
case-insensitive.

However, even in that case, I'm not sure if it's worth keeping track of
a separate marker.

Regards,
    Jeff Davis