On 13.02.25 14:06, jian he wrote:
I didn't solve the out join semantic issue. i am wondering, can we do the virtual generated column expansion in the rewrite stage as is, and wrap the expressions in PHVs if the virtual generated columns come from the nullable side of an outer join.
PlaceHolderVar looks like a fitting mechanism for this. But it's so far a planner node, so it might take some additional consideration if we want to expand where it's used.
Maybe a short-term fix would be to error out if we find ourselves about to expand a Var with varnullingrels != NULL. That would mean you couldn't use a virtual generated column on the nullable output side of an outer join, which is annoying but not fatal, and we could fix it incrementally later.
