fix: fix order by contains count in scalar subquery

src/query/sql/src/planner/optimizer/heuristic/decorrelate/flatten_plan.rs

@@ -39,6 +39,7 @@ use crate::plans::RelOperator;
 use crate::plans::ScalarExpr;
 use crate::plans::ScalarItem;
 use crate::plans::Scan;
+use crate::plans::Sort;
 use crate::plans::UnionAll;
 use crate::BaseTableColumn;
 use crate::ColumnEntry;
@@ -165,9 +166,13 @@ impl SubqueryRewriter {
                 flatten_info,
                 need_cross_join,
             ),
-            RelOperator::Sort(_) => {
-                self.flatten_sort(plan, correlated_columns, flatten_info, need_cross_join)
-            }
+            RelOperator::Sort(sort) => self.flatten_sort(
+                plan,
+                sort,
+                correlated_columns,
+                flatten_info,
+                need_cross_join,
+            ),
 
             RelOperator::Limit(_) => {
                 self.flatten_limit(plan, correlated_columns, flatten_info, need_cross_join)
@@ -487,6 +492,7 @@ impl SubqueryRewriter {
     fn flatten_sort(
         &mut self,
         plan: &SExpr,
+        sort: &Sort,
         correlated_columns: &ColumnSet,
         flatten_info: &mut FlattenInfo,
         need_cross_join: bool,
@@ -498,6 +504,19 @@ impl SubqueryRewriter {
             flatten_info,
             need_cross_join,
         )?;
+        // Check if sort contains `count() or distinct count()`.
+        if sort.items.iter().any(|item| {
+            let metadata = self.metadata.read();
+            let col = metadata.column(item.index);
+            if let ColumnEntry::DerivedColumn(derived_col) = col {
+                // A little tricky here, we'll check if sort items if a count aggregation function later.
+                derived_col.alias.to_lowercase().starts_with("count")
+            } else {
+                false
+            }
+        }) {
+            flatten_info.from_count_func = false;
+        }
         Ok(SExpr::create_unary(
             Arc::new(plan.plan().clone()),
             Arc::new(flatten_plan),

src/query/sql/src/planner/optimizer/heuristic/subquery_rewriter.rs

@@ -294,7 +294,8 @@ impl SubqueryRewriter {
                         .build(),
                 });
 
-                let scalar = if flatten_info.from_count_func {
+                let scalar = if flatten_info.from_count_func && subquery.typ == SubqueryType::Scalar
+                {
                     // convert count aggregate function to `if(count() is not null, count(), 0)`
                     let is_not_null = ScalarExpr::FunctionCall(FunctionCall {
                         span: subquery.span,

tests/sqllogictests/suites/mode/standalone/explain/explain.test

@@ -1591,3 +1591,126 @@ drop table t1;
 
 statement ok
 drop table t2;
+
+statement ok
+create table t1(a int, b int, c varchar(20));
+
+statement ok
+create table t2(a int, b int, c varchar(20));
+
+# scalar subquery and sort plan contains count() agg function.
+query T
+explain select * from t2 where c > (select c from t1 where t1.a = t2.a group by c order by count(a));
+----
+Filter
+├── output columns: [t2.a (#0), t2.b (#1), t2.c (#2)]
+├── filters: [is_true(t2.c (#2) > scalar_subquery_5 (#5))]
+├── estimated rows: 0.00
+└── HashJoin
+    ├── output columns: [t2.a (#0), t2.b (#1), t2.c (#2), t1.c (#5)]
+    ├── join type: LEFT SINGLE
+    ├── build keys: [a (#3)]
+    ├── probe keys: [a (#0)]
+    ├── filters: []
+    ├── estimated rows: 0.00
+    ├── Sort(Build)
+    │   ├── output columns: [t1.c (#5), t1.a (#3), count(a) (#7)]
+    │   ├── sort keys: [count(a) ASC NULLS LAST]
+    │   ├── estimated rows: 0.00
+    │   └── EvalScalar
+    │       ├── output columns: [t1.c (#5), t1.a (#3), count(a) (#7)]
+    │       ├── expressions: [count(a) (#6)]
+    │       ├── estimated rows: 0.00
+    │       └── AggregateFinal
+    │           ├── output columns: [count(a) (#6), t1.c (#5), t1.a (#3)]
+    │           ├── group by: [c, a]
+    │           ├── aggregate functions: [count(a)]
+    │           ├── estimated rows: 0.00
+    │           └── AggregatePartial
+    │               ├── output columns: [count(a) (#6), #_group_by_key]
+    │               ├── group by: [c, a]
+    │               ├── aggregate functions: [count(a)]
+    │               ├── estimated rows: 0.00
+    │               └── Filter
+    │                   ├── output columns: [t1.a (#3), t1.c (#5)]
+    │                   ├── filters: [is_true(t1.a (#3) = a (#3))]
+    │                   ├── estimated rows: 0.00
+    │                   └── TableScan
+    │                       ├── table: default.default.t1
+    │                       ├── output columns: [a (#3), c (#5)]
+    │                       ├── read rows: 0
+    │                       ├── read bytes: 0
+    │                       ├── partitions total: 0
+    │                       ├── partitions scanned: 0
+    │                       ├── push downs: [filters: [is_true(t1.a (#3) = a (#3))], limit: NONE]
+    │                       └── estimated rows: 0.00
+    └── TableScan(Probe)
+        ├── table: default.default.t2
+        ├── output columns: [a (#0), b (#1), c (#2)]
+        ├── read rows: 0
+        ├── read bytes: 0
+        ├── partitions total: 0
+        ├── partitions scanned: 0
+        ├── push downs: [filters: [], limit: NONE]
+        └── estimated rows: 0.00
+
+query T
+explain select * from t2 where c > (select c from t1 where t1.a = t2.a group by c order by count(*));
+----
+Filter
+├── output columns: [t2.a (#0), t2.b (#1), t2.c (#2)]
+├── filters: [is_true(t2.c (#2) > scalar_subquery_5 (#5))]
+├── estimated rows: 0.00
+└── HashJoin
+    ├── output columns: [t2.a (#0), t2.b (#1), t2.c (#2), t1.c (#5)]
+    ├── join type: LEFT SINGLE
+    ├── build keys: [a (#3)]
+    ├── probe keys: [a (#0)]
+    ├── filters: []
+    ├── estimated rows: 0.00
+    ├── Sort(Build)
+    │   ├── output columns: [t1.c (#5), t1.a (#3), COUNT(*) (#7)]
+    │   ├── sort keys: [COUNT(*) ASC NULLS LAST]
+    │   ├── estimated rows: 0.00
+    │   └── EvalScalar
+    │       ├── output columns: [t1.c (#5), t1.a (#3), COUNT(*) (#7)]
+    │       ├── expressions: [COUNT(*) (#6)]
+    │       ├── estimated rows: 0.00
+    │       └── AggregateFinal
+    │           ├── output columns: [COUNT(*) (#6), t1.c (#5), t1.a (#3)]
+    │           ├── group by: [c, a]
+    │           ├── aggregate functions: [count()]
+    │           ├── estimated rows: 0.00
+    │           └── AggregatePartial
+    │               ├── output columns: [COUNT(*) (#6), #_group_by_key]
+    │               ├── group by: [c, a]
+    │               ├── aggregate functions: [count()]
+    │               ├── estimated rows: 0.00
+    │               └── Filter
+    │                   ├── output columns: [t1.a (#3), t1.c (#5)]
+    │                   ├── filters: [is_true(t1.a (#3) = a (#3))]
+    │                   ├── estimated rows: 0.00
+    │                   └── TableScan
+    │                       ├── table: default.default.t1
+    │                       ├── output columns: [a (#3), c (#5)]
+    │                       ├── read rows: 0
+    │                       ├── read bytes: 0
+    │                       ├── partitions total: 0
+    │                       ├── partitions scanned: 0
+    │                       ├── push downs: [filters: [is_true(t1.a (#3) = a (#3))], limit: NONE]
+    │                       └── estimated rows: 0.00
+    └── TableScan(Probe)
+        ├── table: default.default.t2
+        ├── output columns: [a (#0), b (#1), c (#2)]
+        ├── read rows: 0
+        ├── read bytes: 0
+        ├── partitions total: 0
+        ├── partitions scanned: 0
+        ├── push downs: [filters: [], limit: NONE]
+        └── estimated rows: 0.00
+
+statement ok
+drop table t1;
+
+statement ok
+drop table t2;