comphead commented on code in PR #22100:
URL: https://github.com/apache/datafusion/pull/22100#discussion_r3314416746
##########
datafusion/sql/src/select.rs:
##########
@@ -1449,3 +1457,45 @@ fn has_unnest_expr_recursively(expr: &Expr) -> bool {
});
has_unnest
}
+
+/// Walk `select_exprs`, observe every [`Expr::Unnest`] inside them, and
+/// derive the [`NullHandling`] mode for the resulting [`UnnestOptions`].
+///
+/// * No unnest with `outer = true` → [`NullHandling::Drop`] (default SQL
+/// `UNNEST(...)` semantics, matching DuckDB/PostgreSQL).
+/// * Every unnest with `outer = true` →
[`NullHandling::PreserveAndExpandEmpty`]
+/// (Spark `explode_outer(...)` semantics).
+/// * A mix of `outer = true` and `outer = false` in one SELECT → planning
+/// error, because `UnnestOptions` applies per `Unnest` plan node, not
+/// per output column.
+fn collect_unnest_null_handling(expr_groups: &[Vec<Expr>]) ->
Result<NullHandling> {
+ let mut saw_outer = false;
+ let mut saw_inner = false;
+ for group in expr_groups {
+ for expr in group {
+ expr.apply(|e| {
+ if let Expr::Unnest(UnnestExpr { outer, .. }) = e {
+ if *outer {
+ saw_outer = true;
+ } else {
+ saw_inner = true;
+ }
+ }
+ Ok(TreeNodeRecursion::Continue)
+ })?;
+ }
+ }
+ if saw_outer && saw_inner {
Review Comment:
is it possible?
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