On 8/26/25 20:26, Tom Lane wrote:
> Richard Guo <guofenglinux@gmail.com> writes:
>
>> We could then use this function to remove expressions that are known
>> constant from semi_rhs_exprs. And if we find that all expressions
>> in semi_rhs_exprs are known constant (the second loose end you
>> mentioned), we can give up building unique paths and fall back to a
>> traditional JOIN_SEMI.
> Yeah, I was thinking we could just use the paths of the existing
> rel, but really this case means that we'd need to de-dup down
> to a single row. We could maybe do something involving plastering
> LIMIT 1 on top of each input path
Unique node over incoming empty rows seems to act as LIMIT 1, in
particular, it breaks subplan execution after extracting the first row.
Then I see v3 patch covers this case perfectly.
--
Best regard,
Maksim Milyutin
