Garamda commented on code in PR #13511:
URL: https://github.com/apache/datafusion/pull/13511#discussion_r1980817866
##########
datafusion/sql/src/expr/function.rs:
##########
@@ -349,15 +365,49 @@ impl<S: ContextProvider> SqlToRel<'_, S> {
} else {
// User defined aggregate functions (UDAF) have precedence in case
it has the same name as a scalar built-in function
if let Some(fm) = self.context_provider.get_aggregate_meta(&name) {
- let order_by = self.order_by_to_sort_expr(
- order_by,
- schema,
- planner_context,
- true,
- None,
- )?;
- let order_by = (!order_by.is_empty()).then_some(order_by);
- let args = self.function_args_to_expr(args, schema,
planner_context)?;
+ if fm.is_ordered_set_aggregate() && within_group.is_empty() {
+ return plan_err!("WITHIN GROUP clause is required when
calling ordered set aggregate function({})", fm.name());
+ }
+
+ if null_treatment.is_some() &&
!fm.supports_null_handling_clause() {
+ return plan_err!(
+ "[IGNORE | RESPECT] NULLS are not permitted for {}",
+ fm.name()
+ );
+ }
Review Comment:
> One big question we might need to answer before merging is if we need a
migration strategy for this. Because we now require WITHIN GROUP for these
functions, any users who have queries stored outside of DataFusion will
experience breakages that they can't work around. If we want to provide a
migration path, we may need to support having both forms of calling these
functions, as in
>
> SELECT approx_percentile_cont(column_name, 0.75, 100) FROM table_name;
> SELECT approx_percentile_cont(0.75, 100) WITHIN GROUP (ORDER BY
column_name) FROM table_name;
>
> for at least 1 release so folks can migrate their queries.
This is one of the biggest concerns when I started to work on this feature.
If the community decides the migration strategy like that, then I will make
both syntax supported.
Also, I will file an issue to track the plan so that the current syntax can
be excluded as scheduled. (if I am authorized to do so)
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