findepi commented on code in PR #16538:
URL: https://github.com/apache/datafusion/pull/16538#discussion_r2167033810
##########
datafusion/sql/src/expr/function.rs:
##########
@@ -375,6 +375,10 @@ impl<S: ContextProvider> SqlToRel<'_, S> {
return plan_err!("WITHIN GROUP clause is required when
calling ordered set aggregate function({})", fm.name());
}
+ if !fm.is_ordered_set_aggregate() && !within_group.is_empty() {
+ return plan_err!("WITHIN GROUP clause is not permitted for
non-ordered set aggregate function({})", fm.name());
Review Comment:
array_agg is definitely ordered, or order-sensitive
##########
datafusion/sqllogictest/test_files/aggregate.slt:
##########
@@ -7040,3 +7040,7 @@ VALUES
) GROUP BY 1 ORDER BY 1;
----
x 1
+
+statement error DataFusion error: Error during planning: WITHIN GROUP clause
is not permitted for non-ordered set aggregate function\(array_agg\)
+SELECT array_agg(DISTINCT a_varchar) within group (order by a_varchar)
+FROM (VALUES ('a'), ('d'), ('c'), ('a')) t(a_varchar);
Review Comment:
There is no reason for this not to work. Equivalent syntax is already
supported:
```
DataFusion CLI v48.0.0
> SELECT array_agg(DISTINCT a_varchar order by a_varchar)
FROM (VALUES ('a'), ('d'), ('c'), ('a')) t(a_varchar);
+-----------------------------------------------------------------------+
| array_agg(DISTINCT t.a_varchar) ORDER BY [t.a_varchar ASC NULLS LAST] |
+-----------------------------------------------------------------------+
| [a, c, d] |
+-----------------------------------------------------------------------+
```
... and not only in DataFusion
```
trino> SELECT array_agg(DISTINCT a_varchar order by a_varchar)
-> FROM (VALUES ('a'), ('d'), ('c'), ('a')) t(a_varchar);;
_col0
-----------
[a, c, d]
```
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