From c7ae49a269829bb3928f4bc391b1d9301b625d79 Mon Sep 17 00:00:00 2001
From: morrySnow <morrysnow@126.com>
Date: Tue, 20 Aug 2024 19:49:06 +0800
Subject: [PATCH] [fix](Nereids) eliminate union should execute before limit
 push down

other wise:

push limit through union could generate plan:

```
limit
+-- union
    |-- limit
    |   +-- empty relation
    +-- limit
        +-- project
```

and then eliminate union will generate plan:

```
+-- limit
    +-  project
        +-- limit
            +-- project
```

it could not be processed by tranlator correctly
---
 .../doris/nereids/jobs/executor/Rewriter.java | 13 +++++++++++-
 .../push_limit_with_eliminate_union.groovy    | 21 +++++++++++++++++++
 2 files changed, 33 insertions(+), 1 deletion(-)
 create mode 100644 regression-test/suites/nereids_p0/union/push_limit_with_eliminate_union.groovy

diff --git a/fe/fe-core/src/main/java/org/apache/doris/nereids/jobs/executor/Rewriter.java b/fe/fe-core/src/main/java/org/apache/doris/nereids/jobs/executor/Rewriter.java
index d2316ba567bc70..715463b496b3bc 100644
--- a/fe/fe-core/src/main/java/org/apache/doris/nereids/jobs/executor/Rewriter.java
+++ b/fe/fe-core/src/main/java/org/apache/doris/nereids/jobs/executor/Rewriter.java
@@ -118,6 +118,7 @@
 import org.apache.doris.nereids.rules.rewrite.PushDownLimit;
 import org.apache.doris.nereids.rules.rewrite.PushDownLimitDistinctThroughJoin;
 import org.apache.doris.nereids.rules.rewrite.PushDownLimitDistinctThroughUnion;
+import org.apache.doris.nereids.rules.rewrite.PushDownProjectThroughLimit;
 import org.apache.doris.nereids.rules.rewrite.PushDownTopNDistinctThroughJoin;
 import org.apache.doris.nereids.rules.rewrite.PushDownTopNDistinctThroughUnion;
 import org.apache.doris.nereids.rules.rewrite.PushDownTopNThroughJoin;
@@ -422,7 +423,17 @@ public class Rewriter extends AbstractBatchJobExecutor {
                 topic("eliminate",
                         // SORT_PRUNING should be applied after mergeLimit
                         custom(RuleType.ELIMINATE_SORT, EliminateSort::new),
-                        bottomUp(new EliminateEmptyRelation())
+                        bottomUp(
+                                new EliminateEmptyRelation(),
+                                // after eliminate empty relation under union, we could get
+                                // limit
+                                // +-- project
+                                //     +-- limit
+                                //         + project
+                                // so, we need push project through limit to satisfy translator's assumptions
+                                new PushDownFilterThroughProject(),
+                                new PushDownProjectThroughLimit(),
+                                new MergeProjects())
                 ),
                 topic("agg rewrite",
                     // these rules should be put after mv optimization to avoid mv matching fail
diff --git a/regression-test/suites/nereids_p0/union/push_limit_with_eliminate_union.groovy b/regression-test/suites/nereids_p0/union/push_limit_with_eliminate_union.groovy
new file mode 100644
index 00000000000000..1c9604a5ad6e24
--- /dev/null
+++ b/regression-test/suites/nereids_p0/union/push_limit_with_eliminate_union.groovy
@@ -0,0 +1,21 @@
+// 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("push_limit_with_eliminate_union") {
+    // this should not failed for [INTERNAL_ERROR]VSlotRef  have invalid slot id
+    sql """(select 1 limit 0 union all select count() + 1) limit 1;"""
+}