Hi Chris:

On Thu, Dec 1, 2016 at 12:56 PM, Chris Withers <ch...@simplistix.co.uk> wrote:
> So, first observation: if I make room nullable, the exclude constraint does
> not apply for rows that have a room of null. I guess that's to be expected,
> right?

I would expect it, given:

n=> select null=null, null<>null, not (null=null);
 ?column? | ?column? | ?column?
          |          |
(1 row)

Those are nulls, BTW:

n=> select (null=null) is null, (null<>null) is null, (not (null=null)) is null;
 ?column? | ?column? | ?column?
 t        | t        | t
(1 row)

I.e., the same happens with a nullable unique column, you can have one
of each not null values and as many nulls as you want.

SQL null is a strange beast.

Francisco Olarte.

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