itsjunetime commented on code in PR #11994:
URL: https://github.com/apache/datafusion/pull/11994#discussion_r1718844856
##########
datafusion/core/src/datasource/physical_plan/parquet/row_filter.rs:
##########
@@ -243,13 +295,17 @@ impl<'a> TreeNodeRewriter for FilterCandidateBuilder<'a> {
Ok(Transformed::no(node))
}
+ /// After visiting all children, rewrite column references to nulls if
+ /// they are not in the file schema
fn f_up(
&mut self,
expr: Arc<dyn PhysicalExpr>,
) -> Result<Transformed<Arc<dyn PhysicalExpr>>> {
+ // if the expression is a column, is it in the file schema?
if let Some(column) = expr.as_any().downcast_ref::<Column>() {
if self.file_schema.field_with_name(column.name()).is_err() {
- // the column expr must be in the table schema
+ // Replace the column reference with a NULL (using the type
from the table schema)
+ // e.g. `column = 'foo'` is rewritten be transformed to `NULL
= 'foo'`
Review Comment:
This is obviously a much better comment than before, but I think it could be
further improved with an explanation stating why we do this column rewriting,
or what purpose it serves.
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