Re: Proposal: Add a UNIQUE NOT ENFORCED constraint

Hi Jacob,

On Mon, Jan 5, 2026 at 1:34 AM Jacob Jackson <jej(dot)jackson(dot)08(at)gmail(dot)com>
wrote:

>
> In many cases, the idiomatic/generally best way to write a query
> requires a uniqueness check (a SELECT WHERE ... = ANY()/IN or really
> any semi-join when optimized to an inner join, UNION, etc), meaning a
> Unique/HashAggregate node will be added, increasing overhead unless
> there is an explicit unique constraint. An unenforced unique
> constraint would allow developers to use their knowledge of the
> data/previous validation procedures to eliminate the extra node. This
> would also help with documentation/observability tools by providing
> more context on the data without adding overhead.
>
>
I'm not very familiar with the UNIQUE NOT ENFORCED constraint, so apologies
if I make any mistakes here. If we want the query planner to generate an
execution plan as if a column were unique, would setting n_distinct = -1 in
the table statistics achieve the same effect?