From d39bca5ec76a1997c8a048f879eb10ad11a5de3f Mon Sep 17 00:00:00 2001
From: starocean999 <40539150+starocean999@users.noreply.github.com>
Date: Fri, 7 Jul 2023 18:12:28 +0800
Subject: [PATCH] [fix](nereids) don't build cte producer if the consumer is
 empty relation (#21317)

explain WITH cte_0 AS ( SELECT 1 AS a ) SELECT * from cte_0 t1 join cte_0 t2 on true WHERE false;
before:
```
+----------------------------+
| Explain String             |
+----------------------------+
| PLAN FRAGMENT 0            |
|   OUTPUT EXPRS:            |
|     a[#1]                  |
|     a[#2]                  |
|   PARTITION: UNPARTITIONED |
|                            |
|   VRESULT SINK             |
|                            |
|   1:VEMPTYSET              |
|                            |
| PLAN FRAGMENT 1            |
|   OUTPUT EXPRS:            |
|     a[#0]                  |
|   PARTITION: UNPARTITIONED |
|                            |
|   MultiCastDataSinks       |
|                            |
|   0:VUNION                 |
|      constant exprs:       |
|          1                 |
+----------------------------+
```
after:

```
+----------------------------+
| Explain String             |
+----------------------------+
| PLAN FRAGMENT 0            |
|   OUTPUT EXPRS:            |
|     a[#0]                  |
|     a[#1]                  |
|   PARTITION: UNPARTITIONED |
|                            |
|   VRESULT SINK             |
|                            |
|   0:VEMPTYSET              |
+----------------------------+
```
---
 .../rewrite/BuildCTEAnchorAndCTEProducer.java | 23 +++++++++++--------
 .../suites/nereids_syntax_p0/cte.groovy       |  5 ++++
 2 files changed, 18 insertions(+), 10 deletions(-)

diff --git a/fe/fe-core/src/main/java/org/apache/doris/nereids/rules/rewrite/BuildCTEAnchorAndCTEProducer.java b/fe/fe-core/src/main/java/org/apache/doris/nereids/rules/rewrite/BuildCTEAnchorAndCTEProducer.java
index dab88e686e4432..11700ecb7785c3 100644
--- a/fe/fe-core/src/main/java/org/apache/doris/nereids/rules/rewrite/BuildCTEAnchorAndCTEProducer.java
+++ b/fe/fe-core/src/main/java/org/apache/doris/nereids/rules/rewrite/BuildCTEAnchorAndCTEProducer.java
@@ -24,6 +24,7 @@
 import org.apache.doris.nereids.trees.plans.logical.LogicalCTE;
 import org.apache.doris.nereids.trees.plans.logical.LogicalCTEAnchor;
 import org.apache.doris.nereids.trees.plans.logical.LogicalCTEProducer;
+import org.apache.doris.nereids.trees.plans.logical.LogicalEmptyRelation;
 import org.apache.doris.nereids.trees.plans.logical.LogicalPlan;
 import org.apache.doris.nereids.trees.plans.logical.LogicalSubQueryAlias;
 import org.apache.doris.qe.ConnectContext;
@@ -47,17 +48,19 @@ private LogicalPlan rewrite(LogicalPlan p, CascadesContext cascadesContext) {
         }
         LogicalCTE logicalCTE = (LogicalCTE) p;
         LogicalPlan child = (LogicalPlan) logicalCTE.child();
-        for (int i = logicalCTE.getAliasQueries().size() - 1; i >= 0; i--) {
-            LogicalSubQueryAlias s = (LogicalSubQueryAlias) logicalCTE.getAliasQueries().get(i);
-            CTEId id = logicalCTE.findCTEId(s.getAlias());
-            if (cascadesContext.cteReferencedCount(id)
-                    <= ConnectContext.get().getSessionVariable().inlineCTEReferencedThreshold
-                    || !ConnectContext.get().getSessionVariable().getEnablePipelineEngine()) {
-                continue;
+        if (!(child instanceof LogicalEmptyRelation)) {
+            for (int i = logicalCTE.getAliasQueries().size() - 1; i >= 0; i--) {
+                LogicalSubQueryAlias s = (LogicalSubQueryAlias) logicalCTE.getAliasQueries().get(i);
+                CTEId id = logicalCTE.findCTEId(s.getAlias());
+                if (cascadesContext.cteReferencedCount(id)
+                        <= ConnectContext.get().getSessionVariable().inlineCTEReferencedThreshold
+                        || !ConnectContext.get().getSessionVariable().getEnablePipelineEngine()) {
+                    continue;
+                }
+                LogicalCTEProducer logicalCTEProducer = new LogicalCTEProducer(
+                        rewrite((LogicalPlan) s.child(), cascadesContext), id);
+                child = new LogicalCTEAnchor(logicalCTEProducer, child, id);
             }
-            LogicalCTEProducer logicalCTEProducer = new LogicalCTEProducer(
-                    rewrite((LogicalPlan) s.child(), cascadesContext), id);
-            child = new LogicalCTEAnchor(logicalCTEProducer, child, id);
         }
         return child;
     }
diff --git a/regression-test/suites/nereids_syntax_p0/cte.groovy b/regression-test/suites/nereids_syntax_p0/cte.groovy
index d2b6eefa0dbd33..15a7afc9556edb 100644
--- a/regression-test/suites/nereids_syntax_p0/cte.groovy
+++ b/regression-test/suites/nereids_syntax_p0/cte.groovy
@@ -301,5 +301,10 @@ suite("cte") {
         exception = "[cte1] cannot be used more than once"
     }
 
+    explain {
+        sql("WITH cte_0 AS ( SELECT 1 AS a ) SELECT * from cte_0 t1 join cte_0 t2 on true WHERE false;")
+        notContains "MultiCastDataSinks"
+    }
+
 }