ametel01 commented on code in PR #22948:
URL: https://github.com/apache/datafusion/pull/22948#discussion_r3432972869
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datafusion/sql/src/expr/mod.rs:
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@@ -55,6 +57,55 @@ 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<Option<Span>> {
+ if let SQLExpr::Value(ValueWithSpan {
+ value: Value::Null,
+ span,
+ }) = expr
+ {
+ Some(Span::try_from_sqlparser_span(*span))
+ } else {
+ None
+ }
+ }
+
+ fn null_equality_warning(expr: &SQLExpr) -> Option<Diagnostic> {
+ let SQLExpr::BinaryOp { left, op, right } = expr else {
+ return None;
+ };
+
+ let null_span = null_value_span(left).or_else(||
null_value_span(right))?;
+
+ 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,
+ };
+
+ Some(
+ Diagnostic::new_warning(
+ message,
+ Span::try_from_sqlparser_span(expr.span()),
+ )
+ .with_help(help, null_span),
+ )
+ }
+
+ let _ = visit_expressions(predicate, |expr| {
Review Comment:
Fixed in 3b1e9cc5c. The NULL equality warning visitor now tracks subquery
query depth, so the outer predicate pass skips projection expressions inside
subquery bodies while subquery WHERE/JOIN/HAVING predicates are still checked
by their own planning flow. Added regression coverage for both cases.
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