siddubakka commented on code in PR #26164:
URL: https://github.com/apache/datafusion/pull/26164#discussion_r4233180619
##########
datafusion/expr/src/expr_schema.rs:
##########
@@ -435,6 +435,24 @@ impl ExprSchemable for Expr {
Expr::ScalarSubquery(subquery) =>
Ok(scalar_subquery_nullable(subquery)),
Expr::BinaryExpr(BinaryExpr { left, right, op }) => match op {
Operator::IsDistinctFrom | Operator::IsNotDistinctFrom =>
Ok(false),
+ Operator::And => {
+ if contains_is_not_null(left.as_ref(), right.as_ref()) {
Review Comment:
yeah fair point -- so IsNotNull already returns Ok(false) for nullable since
it's always a bool. the thing is when the simplifier turns CASE WHEN x IS NOT
NULL THEN x ELSE false END into x IS NOT NULL AND x, the AND sees that x is
nullable and reports the whole thing as nullable. but semantically it can't be
null -- if x is null then IS NOT NULL(x) is false and alse AND NULL = false.
so the special-casing here is really about AND/OR knowing that an IS NOT NULL
guard makes the other operand safe. happy to explore a different approach if
you have something in mind though!
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