From 23f7f009fb89351eaa946c4cc7aa85380717ff8c Mon Sep 17 00:00:00 2001
From: feiniaofeiafei <53502832+feiniaofeiafei@users.noreply.github.com>
Date: Fri, 11 Oct 2024 11:14:11 +0800
Subject: [PATCH] [fix](Nerieds) column prune should retain at least one column
 for union all  (#41613)

select count(1) from(select 3, 6 union all select 1, 3) t

wrong LogicalUnion plan:

LogicalUnion( qualifier=ALL, outputs=[3#6], regularChildrenOutputs=[], constantExprsList=[[], []], hasPushedFilter=false

this sql will report error in explain, because the logical union outputs
has a slot, but the logical union has no child and has a empty
constantExprList, which is wrong set in column prune.
this pr fixes it by consider when require columns is empty and keep the
min slot and min slot corresponding const expressions.
---
 .../nereids/rules/rewrite/ColumnPruning.java  | 22 +++++++++---------
 .../union_const_expr_column_pruning.groovy    | 23 +++++++++++++++++++
 2 files changed, 34 insertions(+), 11 deletions(-)
 create mode 100644 regression-test/suites/nereids_rules_p0/column_pruning/union_const_expr_column_pruning.groovy

diff --git a/fe/fe-core/src/main/java/org/apache/doris/nereids/rules/rewrite/ColumnPruning.java b/fe/fe-core/src/main/java/org/apache/doris/nereids/rules/rewrite/ColumnPruning.java
index b10a87479f2c95..4a60e94f76f766 100644
--- a/fe/fe-core/src/main/java/org/apache/doris/nereids/rules/rewrite/ColumnPruning.java
+++ b/fe/fe-core/src/main/java/org/apache/doris/nereids/rules/rewrite/ColumnPruning.java
@@ -322,17 +322,6 @@ private LogicalUnion pruneUnionOutput(LogicalUnion union, PruneContext context)
                 extractColumnIndex.add(i);
             }
         }
-        int len = extractColumnIndex.size();
-        ImmutableList.Builder<List<NamedExpression>> prunedConstantExprsList
-                = ImmutableList.builderWithExpectedSize(constantExprsList.size());
-        for (List<NamedExpression> row : constantExprsList) {
-            ImmutableList.Builder<NamedExpression> newRow = ImmutableList.builderWithExpectedSize(len);
-            for (int idx : extractColumnIndex) {
-                newRow.add(row.get(idx));
-            }
-            prunedConstantExprsList.add(newRow.build());
-        }
-
         if (prunedOutputs.isEmpty()) {
             List<NamedExpression> candidates = Lists.newArrayList(originOutput);
             candidates.retainAll(keys);
@@ -341,8 +330,19 @@ private LogicalUnion pruneUnionOutput(LogicalUnion union, PruneContext context)
             }
             NamedExpression minimumColumn = ExpressionUtils.selectMinimumColumn(candidates);
             prunedOutputs = ImmutableList.of(minimumColumn);
+            extractColumnIndex.add(originOutput.indexOf(minimumColumn));
         }
 
+        int len = extractColumnIndex.size();
+        ImmutableList.Builder<List<NamedExpression>> prunedConstantExprsList
+                = ImmutableList.builderWithExpectedSize(constantExprsList.size());
+        for (List<NamedExpression> row : constantExprsList) {
+            ImmutableList.Builder<NamedExpression> newRow = ImmutableList.builderWithExpectedSize(len);
+            for (int idx : extractColumnIndex) {
+                newRow.add(row.get(idx));
+            }
+            prunedConstantExprsList.add(newRow.build());
+        }
         if (prunedOutputs.equals(originOutput)) {
             return union;
         } else {
diff --git a/regression-test/suites/nereids_rules_p0/column_pruning/union_const_expr_column_pruning.groovy b/regression-test/suites/nereids_rules_p0/column_pruning/union_const_expr_column_pruning.groovy
new file mode 100644
index 00000000000000..77d62a2189960b
--- /dev/null
+++ b/regression-test/suites/nereids_rules_p0/column_pruning/union_const_expr_column_pruning.groovy
@@ -0,0 +1,23 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you 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.
+
+suite("const_expr_column_pruning") {
+    sql """SET ignore_shape_nodes='PhysicalDistribute,PhysicalProject'"""
+    // should only keep one column in union
+    sql "select count(1) from(select 3, 6 union all select 1, 3) t"
+    sql "select count(a) from(select 3 a, 6 union all select 1, 3) t"
+}
\ No newline at end of file