yonatan-sevenai commented on code in PR #21593:
URL: https://github.com/apache/datafusion/pull/21593#discussion_r3119150565
##########
datafusion/sql/src/unparser/ast.rs:
##########
@@ -162,9 +162,28 @@ pub struct SelectBuilder {
qualify: Option<ast::Expr>,
value_table_mode: Option<ast::ValueTableMode>,
flavor: Option<SelectFlavor>,
+ /// Counter for generating unique LATERAL FLATTEN aliases within this
SELECT.
+ flatten_alias_counter: usize,
}
impl SelectBuilder {
+ /// Generate a unique alias for a LATERAL FLATTEN relation
+ /// (`_unnest_1`, `_unnest_2`, …). Each call returns a fresh name.
+ pub fn next_flatten_alias(&mut self) -> String {
+ self.flatten_alias_counter += 1;
+ format!("_unnest_{}", self.flatten_alias_counter)
Review Comment:
Hi @goldmedal.
The query you suggested actually ends up emitting a single unnest node in DF
iterating over both arrays.
I did end up adding the test `snowflake_flatten_multiple_unnest_cross_join`
(in `plan_to_sql.rs`) which uses the following query, which also has the
benefit of simulating cartesian product. The two parallel `unnest`s aren't
actually possible in snowflake as each flatten is it's own iteration.
```sql
SELECT a.a, b.b FROM multi_array_table CROSS JOIN UNNEST(column_a) AS a (a)
CROSS JOIN UNNEST(column_b) AS b (b)`
```
which generates the following query
```sql
SELECT "a"."VALUE", "b"."VALUE" FROM "multi_array_table" CROSS JOIN LATERAL
FLATTEN(INPUT => "multi_array_table"."column_a") AS "a" CROSS JOIN LATERAL
FLATTEN(INPUT => "multi_array_table"."column_b") AS "b""
```
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