Disallow order by within ordered-set aggregate functions argument lists (apache#20421)

## Which issue does this PR close?

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- Closes #apache#18281.

## Rationale for this change
This PR fixes incorrect handling of ordered-set aggregate syntax.
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in the issue then this section is not needed.
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your changes and offer better suggestions for fixes.
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## What changes are included in this PR?
- Updated `datafusion/sql/src/expr/function.rs` to return a planning
error when `ORDER BY` is used inline
- Added test coverage in
`datafusion/sqllogictest/test_files/aggregate.slt` to ensure these
invalid forms now return a syntax/planning error

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## Are these changes tested?
Yes, these changes are tested.
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## Are there any user-facing changes?
Yes - this is a public API change.
This query:
```
select quantile_cont(col0, 0.75 order by col0)
from values (1, 3), (2, 2), (3, 1) t(col0, col1);
```
now returns an error: `ORDER BY must be specified using WITHIN GROUP`
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---------

Co-authored-by: Andrew Lamb <andrew@nerdnetworks.org>

Author: cj-zhukov

datafusion/sql/src/expr/function.rs

@@ -542,32 +542,70 @@ impl<S: ContextProvider> SqlToRel<'_, S> {
                 // accept a WITHIN GROUP clause.
                 let supports_within_group = fm.supports_within_group_clause();
 
-                if !within_group.is_empty() && !supports_within_group {
+                // Built-in ordered-set aggregates must also support WITHIN GROUP
+                let is_builtin_ordered_set = matches!(
+                    name.as_str(),
+                    "percentile_cont"
+                        | "quantile_cont"
+                        | "approx_percentile_cont"
+                        | "approx_percentile_cont_with_weight"
+                );
+
+                let supports_within_group =
+                    supports_within_group || is_builtin_ordered_set;
+
+                let mut within_group = within_group;
+                let mut order_by = order_by;
+
+                if supports_within_group
+                    && within_group.is_empty()
+                    && !order_by.is_empty()
+                {
+                    // Inline ORDER BY syntax:
+                    // quantile_cont(value, percentile ORDER BY value)
+                    if args.len() >= 2 {
+                        args.remove(0);
+                        arg_names.remove(0);
+                    }
+
+                    within_group = order_by;
+                    order_by = vec![];
+                }
+
+                if !supports_within_group && !within_group.is_empty() {
                     return plan_err!(
                         "WITHIN GROUP is only supported for ordered-set aggregate functions"
                     );
                 }
 
-                // If the UDAF supports WITHIN GROUP, convert the ordering into
-                // sort expressions and prepend them as unnamed function args.
-                let order_by = if supports_within_group {
-                    let (within_group_sorts, new_args, new_arg_names) = self
-                        .extract_and_prepend_within_group_args(
+                let order_by: Vec<SortExpr> = if supports_within_group {
+                    if !within_group.is_empty() {
+                        // WITHIN GROUP syntax
+                        let sorts = self.order_by_to_sort_expr(
                             within_group,
-                            args,
-                            arg_names,
                             schema,
                             planner_context,
+                            false,
+                            None,
                         )?;
-                    args = new_args;
-                    arg_names = new_arg_names;
-                    within_group_sorts
-                } else {
-                    let order_by = if !order_by.is_empty() {
-                        order_by
+
+                        if sorts.len() != 1 {
+                            return plan_err!(
+                                "Only a single ordering expression is permitted in WITHIN GROUP clause"
+                            );
+                        }
+
+                        // Prepend ordered value expression to args
+                        let value_expr = sorts[0].expr.clone();
+                        arg_names = std::iter::once(None).chain(arg_names).collect();
+                        args = std::iter::once(value_expr).chain(args).collect();
+
+                        sorts
                     } else {
-                        within_group
-                    };
+                        vec![]
+                    }
+                } else {
+                    // Normal aggregate behavior
                     self.order_by_to_sort_expr(
                         order_by,
                         schema,
@@ -867,6 +905,7 @@ impl<S: ContextProvider> SqlToRel<'_, S> {
         Ok((exprs, names))
     }
 
+    #[expect(dead_code)]
     fn extract_and_prepend_within_group_args(
         &self,
         within_group: Vec<OrderByExpr>,

datafusion/sqllogictest/test_files/aggregate.slt

@@ -125,6 +125,36 @@ CREATE TABLE group_median_table_nullable (
 ( 'group1', 125,  32766,  2147483646,  arrow_cast(9223372036854775806,'Int64'),  100,  101,   4294967294, arrow_cast(100,'UInt64'), 3.2,  5.5,   arrow_cast('NAN','Float64'), 0.0004, 0.0004 ),
 ( 'group1', 127,  32767,  2147483647,  arrow_cast(9223372036854775807,'Int64'),  255,  65535, 4294967295, 18446744073709551615,     2.2,  2.2,   arrow_cast('NAN','Float64'), 0.0005, 0.0005 )
 
+query R
+select quantile_cont(col0, 0.75 order by col0)
+from values (1, 3), (2, 2), (3, 1) t(col0, col1);
+----
+2.5
+
+query R
+select quantile_cont(col0, 0.75 order by col0 desc)
+from values (1, 3), (2, 2), (3, 1) t(col0, col1);
+----
+1.5
+
+query R
+select quantile_cont(0.75 order by col0)
+from values (1, 3), (2, 2), (3, 1) t(col0, col1);
+----
+2.5
+
+query R
+select quantile_cont(0.75 order by col0 desc)
+from values (1, 3), (2, 2), (3, 1) t(col0, col1);
+----
+1.5
+
+query R
+select quantile_cont(0.75) within group (order by col0)
+from values (1), (2), (3) t(col0);
+----
+2.5
+
 #######
 # Error tests
 #######