jayzhan211 commented on code in PR #11577:
URL: https://github.com/apache/datafusion/pull/11577#discussion_r1774868527
##########
datafusion/sql/src/utils.rs:
##########
@@ -309,6 +315,269 @@ pub(crate) fn transform_bottom_unnests(
.collect::<Vec<_>>())
}
+/*
+This is only usedful when used with transform down up
+A full example of how the transformation works:
+ */
+struct RecursiveUnnestRewriter<'a> {
+ input_schema: &'a DFSchemaRef,
+ root_expr: &'a Expr,
+ // useful to detect which child expr is a part of/ not a part of unnest
operation
+ top_most_unnest: Option<Unnest>,
+ consecutive_unnest: Vec<Option<Unnest>>,
+ inner_projection_exprs: &'a mut Vec<Expr>,
+ columns_unnestings: &'a mut Vec<(Column, ColumnUnnestType)>,
+ transformed_root_exprs: Option<Vec<Expr>>,
+}
+impl<'a> RecursiveUnnestRewriter<'a> {
+ /// This struct stores the history of expr
+ /// during its tree-traversal with a notation of
+ /// \[None,**Unnest(exprA)**,**Unnest(exprB)**,None,None\]
+ /// then this function will returns \[**Unnest(exprA)**,**Unnest(exprB)**\]
+ ///
+ /// The first item will be the inner most expr
+ fn get_latest_consecutive_unnest(&self) -> Vec<Unnest> {
+ self.consecutive_unnest
+ .iter()
+ .rev()
+ .skip_while(|item| item.is_none())
+ .take_while(|item| item.is_some())
+ .to_owned()
+ .cloned()
+ .map(|item| item.unwrap())
+ .collect()
+ }
+
+ fn transform(
+ &mut self,
+ level: usize,
+ alias_name: String,
+ expr_in_unnest: &Expr,
+ struct_allowed: bool,
+ ) -> Result<Vec<Expr>> {
+ let inner_expr_name = expr_in_unnest.schema_name().to_string();
+
+ // Full context, we are trying to plan the execution as
InnerProjection->Unnest->OuterProjection
+ // inside unnest execution, each column inside the inner projection
+ // will be transformed into new columns. Thus we need to keep track of
these placeholding column names
+ // let placeholder_name = unnest_expr.display_name()?;
Review Comment:
seems like leftover
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