ametel01 commented on code in PR #22948:
URL: https://github.com/apache/datafusion/pull/22948#discussion_r3427203958
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datafusion/sql/src/expr/mod.rs:
##########
@@ -55,6 +55,99 @@ mod unary_op;
mod value;
impl<S: ContextProvider> SqlToRel<'_, S> {
+ pub(crate) fn warn_on_null_equality_predicate(&self, predicate: &SQLExpr) {
+ fn null_value_span(expr: &SQLExpr) -> Option<Span> {
+ match expr {
+ SQLExpr::Value(ValueWithSpan {
+ value: Value::Null,
+ span,
+ }) => Span::try_from_sqlparser_span(*span),
+ _ => None,
+ }
+ }
+
+ fn null_equality_warning(expr: &SQLExpr) -> Option<Diagnostic> {
+ let SQLExpr::BinaryOp { left, op, right } = expr else {
+ return None;
+ };
+
+ let (message, help) = match op {
+ BinaryOperator::Eq => (
+ "comparison with NULL using `=` always evaluates to NULL",
+ "use `IS NULL` to check for NULL values",
+ ),
+ BinaryOperator::NotEq => (
+ "comparison with NULL using `<>` always evaluates to NULL",
+ "use `IS NOT NULL` to check for non-NULL values",
+ ),
+ _ => return None,
+ };
+
+ let null_span = null_value_span(left).or_else(||
null_value_span(right));
+ null_span.map(|null_span| {
+ Diagnostic::new_warning(
+ message,
+ Span::try_from_sqlparser_span(expr.span()),
+ )
+ .with_help(help, Some(null_span))
+ })
+ }
+
+ fn collect_null_equality_warnings(
+ expr: &SQLExpr,
+ warnings: &mut Vec<Diagnostic>,
+ ) {
+ if let Some(warning) = null_equality_warning(expr) {
+ warnings.push(warning);
+ }
+
+ match expr {
+ SQLExpr::BinaryOp { left, right, .. }
+ | SQLExpr::IsDistinctFrom(left, right)
+ | SQLExpr::IsNotDistinctFrom(left, right) => {
+ collect_null_equality_warnings(left, warnings);
+ collect_null_equality_warnings(right, warnings);
+ }
+ SQLExpr::Nested(expr)
+ | SQLExpr::UnaryOp { expr, .. }
+ | SQLExpr::IsFalse(expr)
+ | SQLExpr::IsNotFalse(expr)
+ | SQLExpr::IsTrue(expr)
+ | SQLExpr::IsNotTrue(expr)
+ | SQLExpr::IsUnknown(expr)
+ | SQLExpr::IsNotUnknown(expr)
+ | SQLExpr::OuterJoin(expr)
+ | SQLExpr::Prior(expr) => {
+ collect_null_equality_warnings(expr, warnings);
+ }
+ SQLExpr::Case {
+ operand,
+ conditions,
+ else_result,
+ ..
+ } => {
+ if let Some(operand) = operand {
+ collect_null_equality_warnings(operand, warnings);
+ }
+ for condition in conditions {
+ collect_null_equality_warnings(&condition.condition,
warnings);
+ collect_null_equality_warnings(&condition.result,
warnings);
+ }
+ if let Some(else_result) = else_result {
+ collect_null_equality_warnings(else_result, warnings);
+ }
+ }
+ _ => {}
+ }
+ }
+
+ let mut warnings = vec![];
+ collect_null_equality_warnings(predicate, &mut warnings);
+ for warning in warnings {
+ self.add_warning(warning);
+ }
+ }
Review Comment:
Fixed. The warning pass now uses sqlparser::ast::visit_expressions instead
of a hand-written subset traversal, so wrapped predicate expressions are
covered. Added
test_eq_null_warning_under_is_null_predicate.
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