xudong963 commented on code in PR #17088:
URL: https://github.com/apache/datafusion/pull/17088#discussion_r2265983998
##########
datafusion/expr-common/src/operator.rs:
##########
@@ -328,6 +328,55 @@ impl Operator {
Operator::Multiply | Operator::Divide | Operator::Modulo => 45,
}
}
+
+ /// Returns true if the `Expr::BinaryOperator` with this operator
+ /// is guaranteed to return null if either side is null.
+ pub fn returns_null_on_null(&self) -> bool {
+ match self {
+ Operator::Eq
+ | Operator::NotEq
+ | Operator::Lt
+ | Operator::LtEq
+ | Operator::Gt
+ | Operator::GtEq
+ | Operator::Plus
+ | Operator::Minus
+ | Operator::Multiply
+ | Operator::Divide
+ | Operator::Modulo
+ | Operator::RegexMatch
+ | Operator::RegexIMatch
+ | Operator::RegexNotMatch
+ | Operator::RegexNotIMatch
+ | Operator::LikeMatch
+ | Operator::ILikeMatch
+ | Operator::NotLikeMatch
+ | Operator::NotILikeMatch
+ | Operator::BitwiseAnd
+ | Operator::BitwiseOr
+ | Operator::BitwiseXor
+ | Operator::BitwiseShiftRight
+ | Operator::BitwiseShiftLeft
+ | Operator::AtArrow
+ | Operator::ArrowAt
+ | Operator::Arrow
+ | Operator::LongArrow
+ | Operator::HashArrow
+ | Operator::HashLongArrow
+ | Operator::AtAt
+ | Operator::IntegerDivide
+ | Operator::HashMinus
+ | Operator::AtQuestion
+ | Operator::Question
+ | Operator::QuestionAnd
+ | Operator::QuestionPipe => true,
+ Operator::Or
+ | Operator::And
+ | Operator::IsDistinctFrom
+ | Operator::IsNotDistinctFrom
+ | Operator::StringConcat => false,
Review Comment:
I recommend adding such comments, three-valued boolean logic is alway
ignored.
```suggestion
// In SQL's three-valued boolean logic (TRUE, FALSE, NULL),
these operators do not always return NULL
// when either operand is NULL:
// - For logical OR: If one side is TRUE, the result is TRUE
even if the other side is NULL.
// - For logical AND: If one side is FALSE, the result is FALSE
even if the other side is NULL.
// - For IS DISTINCT FROM / IS NOT DISTINCT FROM: These always
return TRUE or FALSE, never NULL,
// even if either operand is NULL.
// - For string concatenation: Some SQL dialects treat NULL as
an empty string, so the result may not be NULL.
// Because the result is not guaranteed to be NULL when either
side is NULL, these operators return false here.
Operator::Or
| Operator::And
| Operator::IsDistinctFrom
| Operator::IsNotDistinctFrom
| Operator::StringConcat => false,
```
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