pepijnve commented on code in PR #17813:
URL: https://github.com/apache/datafusion/pull/17813#discussion_r2415726130
##########
datafusion/expr/src/expr_schema.rs:
##########
@@ -647,6 +679,246 @@ impl ExprSchemable for Expr {
}
}
+/// Represents the possible values for SQL's three valued logic.
+/// `Option<bool>` is not used for this since `None` is used to represent
+/// inconclusive answers already.
+enum TriStateBool {
+ True,
+ False,
+ Uncertain,
+}
+
+impl TryFrom<&ScalarValue> for TriStateBool {
+ type Error = DataFusionError;
+
+ fn try_from(value: &ScalarValue) -> std::result::Result<Self, Self::Error>
{
+ match value {
+ ScalarValue::Null => Ok(TriStateBool::Uncertain),
+ ScalarValue::Boolean(b) => Ok(match b {
+ None => TriStateBool::Uncertain,
+ Some(true) => TriStateBool::True,
+ Some(false) => TriStateBool::False,
+ }),
+ _ => Self::try_from(&value.cast_to(&DataType::Boolean)?),
+ }
+ }
+}
+
+struct WhenThenConstEvaluator<'a> {
+ then_expr: &'a Expr,
+ input_schema: &'a dyn ExprSchema,
+}
+
+impl WhenThenConstEvaluator<'_> {
+ /// Attempts to const evaluate the given predicate.
+ /// Returns a `Some` value containing the const result if so; otherwise
returns `None`.
+ fn const_eval_predicate(&self, predicate: &Expr) -> Option<TriStateBool> {
+ match predicate {
+ // Literal null is equivalent to boolean uncertain
+ Expr::Literal(scalar, _) => TriStateBool::try_from(scalar).ok(),
Review Comment:
My rationale here was that, since nullability analysis must to be
infallible, that it would be ok to return `None` here which means "answer is
undefined". If you were to actually try to evaluate the expression it will most
likely cause a runtime error at that point so inaccurate nullability is the
least of your concerns.
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