diff --git a/src/frontend/planner_test/tests/testdata/project.yaml b/src/frontend/planner_test/tests/testdata/project.yaml
index 6de27ff36553..9fe50fb7a38b 100644
--- a/src/frontend/planner_test/tests/testdata/project.yaml
+++ b/src/frontend/planner_test/tests/testdata/project.yaml
@@ -3,9 +3,6 @@
     select 1 as k, 2 as v;
   batch_plan: |
     BatchValues { rows: [[1:Int32, 2:Int32]] }
-- name: Project over union all of nested project over union all, now, and simple agg
-  sql: |
-    create table t(v int);
-    select 'abc', 1, 1.4 as k from (select 1 as k, 2 from (select 1, 2 union all select 3, 4) union all select * from (select 3, 4) union all select 100, 200 from (select now(), now() - interval '1 hour') union all select count(*)::int, sum(v)::int from t);
+- sql: select 'abc', 1, 1.4 as k from (select 1 as k, 2 from (select 1, 2 union all select 3, 4) union all select * from (select 3, 4) union all select 100, 200 from (select now(), now() - interval '1 hour'));
   batch_plan: |
-    BatchValues { rows: [['abc':Varchar, 1:Int32, 1.4:Decimal], ['abc':Varchar, 1:Int32, 1.4:Decimal], ['abc':Varchar, 1:Int32, 1.4:Decimal], ['abc':Varchar, 1:Int32, 1.4:Decimal], ['abc':Varchar, 1:Int32, 1.4:Decimal]] }
+    BatchValues { rows: [['abc':Varchar, 1:Int32, 1.4:Decimal], ['abc':Varchar, 1:Int32, 1.4:Decimal], ['abc':Varchar, 1:Int32, 1.4:Decimal], ['abc':Varchar, 1:Int32, 1.4:Decimal]] }
diff --git a/src/frontend/planner_test/tests/testdata/union.yaml b/src/frontend/planner_test/tests/testdata/union.yaml
index 1b221281526b..b904226c0f06 100644
--- a/src/frontend/planner_test/tests/testdata/union.yaml
+++ b/src/frontend/planner_test/tests/testdata/union.yaml
@@ -206,46 +206,22 @@
 - sql: |
     select 1 union all select 1
   optimized_logical_plan: |
-    LogicalUnion { all: true }
-    ├─LogicalValues { rows: [[1:Int32]], schema: Schema { fields: [1:Int32:Int32] } }
-    └─LogicalValues { rows: [[1:Int32]], schema: Schema { fields: [1:Int32:Int32] } }
+    LogicalValues { rows: [[1:Int32], [1:Int32]], schema: Schema { fields: [1:Int32:Int32] } }
   batch_plan: |
-    BatchUnion { all: true }
-    ├─BatchValues { rows: [[1:Int32]] }
-    └─BatchValues { rows: [[1:Int32]] }
+    BatchValues { rows: [[1:Int32], [1:Int32]] }
 - sql: |
     select 1 union all select 2 union all select 3 union all select 4 union all select 5
   optimized_logical_plan: |
-    LogicalUnion { all: true }
-    ├─LogicalValues { rows: [[1:Int32]], schema: Schema { fields: [1:Int32:Int32] } }
-    ├─LogicalValues { rows: [[2:Int32]], schema: Schema { fields: [2:Int32:Int32] } }
-    ├─LogicalValues { rows: [[3:Int32]], schema: Schema { fields: [3:Int32:Int32] } }
-    ├─LogicalValues { rows: [[4:Int32]], schema: Schema { fields: [4:Int32:Int32] } }
-    └─LogicalValues { rows: [[5:Int32]], schema: Schema { fields: [5:Int32:Int32] } }
+    LogicalValues { rows: [[1:Int32], [2:Int32], [3:Int32], [4:Int32], [5:Int32]], schema: Schema { fields: [1:Int32:Int32] } }
   batch_plan: |
-    BatchUnion { all: true }
-    ├─BatchValues { rows: [[1:Int32]] }
-    ├─BatchValues { rows: [[2:Int32]] }
-    ├─BatchValues { rows: [[3:Int32]] }
-    ├─BatchValues { rows: [[4:Int32]] }
-    └─BatchValues { rows: [[5:Int32]] }
+    BatchValues { rows: [[1:Int32], [2:Int32], [3:Int32], [4:Int32], [5:Int32]] }
 - sql: |
-    select 1 union select 2 union select 3 union select 4 union select 5
+    select 1 union select 2 union select 3 union select 4 union select 5 union select 5
   optimized_logical_plan: |
     LogicalAgg { group_key: [1:Int32], aggs: [] }
-    └─LogicalUnion { all: true }
-      ├─LogicalValues { rows: [[1:Int32]], schema: Schema { fields: [1:Int32:Int32] } }
-      ├─LogicalValues { rows: [[2:Int32]], schema: Schema { fields: [2:Int32:Int32] } }
-      ├─LogicalValues { rows: [[3:Int32]], schema: Schema { fields: [3:Int32:Int32] } }
-      ├─LogicalValues { rows: [[4:Int32]], schema: Schema { fields: [4:Int32:Int32] } }
-      └─LogicalValues { rows: [[5:Int32]], schema: Schema { fields: [5:Int32:Int32] } }
+    └─LogicalValues { rows: [[1:Int32], [2:Int32], [3:Int32], [4:Int32], [5:Int32], [5:Int32]], schema: Schema { fields: [1:Int32:Int32] } }
   batch_plan: |
     BatchExchange { order: [], dist: Single }
     └─BatchHashAgg { group_key: [1:Int32], aggs: [] }
       └─BatchExchange { order: [], dist: HashShard(1:Int32) }
-        └─BatchUnion { all: true }
-          ├─BatchValues { rows: [[1:Int32]] }
-          ├─BatchValues { rows: [[2:Int32]] }
-          ├─BatchValues { rows: [[3:Int32]] }
-          ├─BatchValues { rows: [[4:Int32]] }
-          └─BatchValues { rows: [[5:Int32]] }
+        └─BatchValues { rows: [[1:Int32], [2:Int32], [3:Int32], [4:Int32], [5:Int32], [5:Int32]] }
diff --git a/src/frontend/src/optimizer/mod.rs b/src/frontend/src/optimizer/mod.rs
index 181d82a7decb..caf076f64dfd 100644
--- a/src/frontend/src/optimizer/mod.rs
+++ b/src/frontend/src/optimizer/mod.rs
@@ -408,6 +408,7 @@ impl PlanRoot {
                 ProjectMergeRule::create(),
                 ProjectEliminateRule::create(),
                 TrivialProjectToValuesRule::create(),
+                UnionInputValuesMergeRule::create(),
                 // project-join merge should be applied after merge
                 // eliminate and to values
                 ProjectJoinMergeRule::create(),
@@ -424,6 +425,7 @@ impl PlanRoot {
                 ProjectMergeRule::create(),
                 ProjectEliminateRule::create(),
                 TrivialProjectToValuesRule::create(),
+                UnionInputValuesMergeRule::create(),
             ],
             ApplyOrder::TopDown,
         );
diff --git a/src/frontend/src/optimizer/rule/mod.rs b/src/frontend/src/optimizer/rule/mod.rs
index de39488b5536..7b91e0af4b4a 100644
--- a/src/frontend/src/optimizer/rule/mod.rs
+++ b/src/frontend/src/optimizer/rule/mod.rs
@@ -87,6 +87,8 @@ mod stream;
 pub use stream::filter_with_now_to_join_rule::*;
 mod trivial_project_to_values_rule;
 pub use trivial_project_to_values_rule::*;
+mod union_input_values_merge_rule;
+pub use union_input_values_merge_rule::*;
 
 #[macro_export]
 macro_rules! for_all_rules {
@@ -121,6 +123,7 @@ macro_rules! for_all_rules {
             ,{FilterWithNowToJoinRule}
             ,{TopNOnIndexRule}
             ,{TrivialProjectToValuesRule}
+            ,{UnionInputValuesMergeRule}
         }
     };
 }
diff --git a/src/frontend/src/optimizer/rule/union_input_values_merge_rule.rs b/src/frontend/src/optimizer/rule/union_input_values_merge_rule.rs
new file mode 100644
index 000000000000..8119b8847b60
--- /dev/null
+++ b/src/frontend/src/optimizer/rule/union_input_values_merge_rule.rs
@@ -0,0 +1,40 @@
+// Copyright 2023 RisingWave Labs
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use super::{BoxedRule, Rule};
+use crate::optimizer::plan_node::LogicalValues;
+use crate::optimizer::{PlanRef, PlanTreeNode};
+
+pub struct UnionInputValuesMergeRule {}
+impl Rule for UnionInputValuesMergeRule {
+    fn apply(&self, plan: PlanRef) -> Option<PlanRef> {
+        let union = plan.as_logical_union()?;
+        // !union.all() is already handled by [`UnionToDistinctRule`]
+        if !union.all() {
+            return None;
+        }
+
+        let mut rows = vec![];
+        for v in union.inputs() {
+            rows.extend_from_slice(v.as_logical_values()?.rows());
+        }
+        Some(LogicalValues::new(rows, union.schema().clone(), union.ctx()).into())
+    }
+}
+
+impl UnionInputValuesMergeRule {
+    pub fn create() -> BoxedRule {
+        Box::new(UnionInputValuesMergeRule {})
+    }
+}