> I think we might want the "*=" operator treat NULL as not equal to NULL and
> this is why we add "IS NOT NULL" to the duplicate detection query.
>
> Your patch treats NULL as equal to NULL, which is different from the SQL
> standard, may confuse users.
>
> So I think we should make the "*=" operator treat NULL as not equal to NULL
> or add a new operator to implement it. Thoughts?
Attach a patch. I add a new built-in function called record_image_eq_variant
which considers two NULLs not equal so that each row can match at most one
row during the full join.
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Regards,
ChangAo Chen