Re: Multi-column distinctness.

I wrote:
> Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> writes:
>> The problem is that the actual syntax is ADD [COLUMN], so we can't
>> simply use ADD STATISTICS as that would mean a conflict in the grammar.
>> Resolving it means either making COLUMN non-optional, or adding
>> STATISTICS to reserved keywords - both options break existing code.

> I'm unconvinced that it cannot be made to work.

Specifically, this works just fine for me as a variant of alter_table_cmd:

| ADD_P STATISTICS ON '(' name_list ')'

and I can get this to work too

| DROP STATISTICS ON '(' name_list ')'

if I expand out the "DROP opt_column" productions to be two separate
productions with and without COLUMN, as was done long ago for ADD COLUMN.

These also work without ON, actually, though it does not work to leave out
the parens. (I think that has to do with the conflict against multiple
ALTER TABLE subcommands, not against ADD COLUMN.)

It doesn't look like we could easily stick a "name" in between STATISTICS
and ON, but I'm unconvinced that that's necessary. Can't we just insist
that there be only one statistics declaration for a given column list?

regards, tom lane