RE: unique index with several columns

Sorry, mixed the lines up:

create unique index idx on t ((
case
when c1 is null and c2 is null then null
when c1 is null and c2 is not null then ARRAY[null,c2]
when c1 is not null and c2 is null then ARRAY[c1,null]
else ARRAY[c1,c2]
end
));

This could be generically extended to an arbitrary number of columns by counting the number of null column values in a separate function.

-----Original Message-----
From: Klaus Kaisersberger <woodconsult(at)outlook(dot)de>
Sent: Friday, March 4, 2022 7:57 PM
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>; Alexey M Boltenkov <padrebolt(at)yandex(dot)ru>
Cc: Voillequin, Jean-Marc <Jean-Marc(dot)Voillequin(at)moodys(dot)com>; David G. Johnston <david(dot)g(dot)johnston(at)gmail(dot)com>; pgsql-sql(at)lists(dot)postgresql(dot)org
Subject: RE: unique index with several columns

This should solve the task:

create unique index idx on t ((
case
when c1 is null and c2 is null then null
when c1 is null and c2 is not null then '{c2}'
when c1 is not null and c2 is null then '{c1}'
else '{c1,c2}'
end));

-----Original Message-----
From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Sent: Friday, March 4, 2022 7:32 PM
To: Alexey M Boltenkov <padrebolt(at)yandex(dot)ru>
Cc: Voillequin, Jean-Marc <Jean-Marc(dot)Voillequin(at)moodys(dot)com>; David G. Johnston <david(dot)g(dot)johnston(at)gmail(dot)com>; pgsql-sql(at)lists(dot)postgresql(dot)org
Subject: Re: unique index with several columns

Alexey M Boltenkov <padrebolt(at)yandex(dot)ru> writes:
> You need the new v15 feature:
> NULLS [NOT] DISTINCT

That won't replicate the behavior shown by the OP though.
In particular, not the weird inconsistency for all-null rows.

regards, tom lane