goldmedal commented on code in PR #13824:
URL: https://github.com/apache/datafusion/pull/13824#discussion_r1894582093
##########
datafusion/sql/src/unparser/rewrite.rs:
##########
@@ -257,6 +267,43 @@ pub(super) fn subquery_alias_inner_query_and_columns(
(outer_projections.input.as_ref(), columns)
}
+/// Try to find the column alias for UNNEST in the inner projection.
+/// For example:
+/// ```sql
+/// SELECT * FROM t1 CROSS JOIN UNNEST(t1.c1) AS u(c1)
+/// ```
+/// The above query will be parsed into the following plan:
+/// ```text
+/// Projection: *
+/// Cross Join:
+/// SubqueryAlias: t1
+/// TableScan: t
+/// SubqueryAlias: u
+/// Subquery:
+/// Projection: UNNEST(outer_ref(t1.c1)) AS c1
+/// Projection: __unnest_placeholder(outer_ref(t1.c1),depth=1) AS
UNNEST(outer_ref(t1.c1))
+/// Unnest: lists[__unnest_placeholder(outer_ref(t1.c1))|depth=1]
structs[]
+/// Projection: outer_ref(t1.c1) AS
__unnest_placeholder(outer_ref(t1.c1))
+/// EmptyRelation
+/// ```
+/// The function will return the inner projection and the column alias `c1` if
the column name
+/// starts with `UNNEST(` (the `Display` result of [Expr::Unnest]) in the
inner projection.
+pub(super) fn find_unnest_column_alias(
+ plan: &LogicalPlan,
+) -> (&LogicalPlan, Option<String>) {
+ if let LogicalPlan::Projection(projection) = plan {
+ if projection.expr.len() != 1 {
+ return (plan, None);
+ }
+ if let Some(Expr::Alias(alias)) = projection.expr.first() {
+ if alias.expr.schema_name().to_string().starts_with("UNNEST(") {
Review Comment:
No, it's not an `Expr::Unnest`. The full plan is
```
/// SubqueryAlias: u
/// Subquery:
/// Projection: UNNEST(outer_ref(t1.c1)) AS c1
/// Projection: __unnest_placeholder(outer_ref(t1.c1),depth=1) AS
UNNEST(outer_ref(t1.c1))
/// Unnest:
lists[__unnest_placeholder(outer_ref(t1.c1))|depth=1] structs[]
/// Projection: outer_ref(t1.c1) AS
__unnest_placeholder(outer_ref(t1.c1))
/// EmptyRelation
```
It's a column pointing to an alias of its child. The alias is built from an
expression `schema_name`.
https://github.com/apache/datafusion/blob/ede665b212ec5e3a673986424103645bcb49e3bc/datafusion/sql/src/utils.rs#L400
I think there is a similar issue for
https://github.com/apache/datafusion/pull/13824#discussion_r1893427907.
Maybe we can have a constant for the display result of `UNNEST`.
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