On 2/7/21 01:56, Hywel Carver wrote:
On Wed, Jun 30, 2021 at 12:21 PM Andrey Lepikhov
<a.lepik...@postgrespro.ru <mailto:a.lepik...@postgrespro.ru>> wrote:
I think, here we could ask more general question: do we want to
remove a
'IS NOT NULL' clause from the clause list if the rest of the list
implicitly implies it?
My suggestion was not to remove it, but to avoid adding it in the first
place. When your optimisation has found a join on a group of columns
under a uniqueness constraint, you would do something like this (forgive
the pseudo-code)
foreach(column, join_clause) {
if(column.nullable) { // This condition is what I'm suggesting is added
add_null_test(column, IS_NOT_NULL);
}
}
But it may be that that's not possible or practical at this point in the
code.
I think, such option will require to implement a new machinery to prove
that arbitrary column couldn't produce NULL value.
--
regards,
Andrey Lepikhov
Postgres Professional
