irenjj commented on PR #17110:
URL: https://github.com/apache/datafusion/pull/17110#issuecomment-3230232039

   > duckdb has a notion of `PropagatesNullValues`, i wonder if we have some 
thing similar
   > 
   > ```
   > impl ExprSchemable for Expr {
   >     fn nullable(&self, input_schema: &dyn ExprSchema) -> Result<bool> {
   > ```
   > 
   > we have something like this, but they are quite different i believe
   
   We can follow the main function in duckdb:
   ```cpp
   bool Expression::PropagatesNullValues() const {
        if (type == ExpressionType::OPERATOR_IS_NULL || type == 
ExpressionType::OPERATOR_IS_NOT_NULL ||
            type == ExpressionType::COMPARE_NOT_DISTINCT_FROM || type == 
ExpressionType::COMPARE_DISTINCT_FROM ||
            type == ExpressionType::CONJUNCTION_OR || type == 
ExpressionType::CONJUNCTION_AND ||
            type == ExpressionType::OPERATOR_COALESCE || type == 
ExpressionType::CASE_EXPR) {
                return false;
        }
        bool propagate_null_values = true;
        ExpressionIterator::EnumerateChildren(*this, [&](const Expression 
&child) {
                if (!child.PropagatesNullValues()) {
                        propagate_null_values = false;
                }
        });
        return propagate_null_values;
   }
   ``


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