Re: Fix optimization of foreign-key on update actions - Mailing list pgsql-hackers

On 06/02/2019 12:23, Andrew Gierth wrote:
> Two values which are sql-equal but not identical, such as two strings in
> a case-insensitive collation that differ only by case, are
> distinguishable in some contexts but not others, so what context
> actually applies to the quoted rule?
> 
> I think the only reasonable interpretation is that it should use the
> same kind of distinctness that is being used by the unique constraint
> and the equality comparison that define whether the FK is satisfied.

By that logic, a command such as

    UPDATE t1 SET x = '0' WHERE x = '-0';

could be optimized away as a noop, because in that world there is no
construct by which you can prove whether the update happened.

I think that would not be satisfactory.

-- 
Peter Eisentraut              http://www.2ndQuadrant.com/
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