From 3f20cf145672b23f5b55053b0ecde18e38942d76 Mon Sep 17 00:00:00 2001
From: starocean999 <40539150+starocean999@users.noreply.github.com>
Date: Fri, 1 Dec 2023 18:40:06 +0800
Subject: [PATCH] [fix](nereids)set operation's result type is wrong if decimal
 overflows (#27870)

---
 .../plans/logical/LogicalSetOperation.java    | 22 ++++++++++++++-----
 .../nereids_p0/datatype/test_cast.groovy      | 19 ++++++++++++++++
 2 files changed, 36 insertions(+), 5 deletions(-)

diff --git a/fe/fe-core/src/main/java/org/apache/doris/nereids/trees/plans/logical/LogicalSetOperation.java b/fe/fe-core/src/main/java/org/apache/doris/nereids/trees/plans/logical/LogicalSetOperation.java
index dd392ad16b..0a3a29e1ef 100644
--- a/fe/fe-core/src/main/java/org/apache/doris/nereids/trees/plans/logical/LogicalSetOperation.java
+++ b/fe/fe-core/src/main/java/org/apache/doris/nereids/trees/plans/logical/LogicalSetOperation.java
@@ -17,6 +17,7 @@
 
 package org.apache.doris.nereids.trees.plans.logical;
 
+import org.apache.doris.catalog.ScalarType;
 import org.apache.doris.catalog.Type;
 import org.apache.doris.nereids.exceptions.AnalysisException;
 import org.apache.doris.nereids.memo.GroupExpression;
@@ -251,10 +252,21 @@ public abstract class LogicalSetOperation extends AbstractLogicalPlan implements
             }
             return new StructType(commonFields.build());
         }
-        return DataType.fromCatalogType(Type.getAssignmentCompatibleType(
-                left.toCatalogDataType(),
-                right.toCatalogDataType(),
-                false,
-                SessionVariable.getEnableDecimal256()));
+        boolean enableDecimal256 = SessionVariable.getEnableDecimal256();
+        Type resultType = Type.getAssignmentCompatibleType(left.toCatalogDataType(),
+                right.toCatalogDataType(), false, enableDecimal256);
+        if (resultType.isDecimalV3()) {
+            int oldPrecision = resultType.getPrecision();
+            int oldScale = resultType.getDecimalDigits();
+            int integerPart = oldPrecision - oldScale;
+            int maxPrecision = enableDecimal256 ? ScalarType.MAX_DECIMAL256_PRECISION
+                    : ScalarType.MAX_DECIMAL128_PRECISION;
+            if (oldPrecision > maxPrecision) {
+                int newScale = maxPrecision - integerPart;
+                resultType =
+                        ScalarType.createDecimalType(maxPrecision, newScale < 0 ? 0 : newScale);
+            }
+        }
+        return DataType.fromCatalogType(resultType);
     }
 }
diff --git a/regression-test/suites/nereids_p0/datatype/test_cast.groovy b/regression-test/suites/nereids_p0/datatype/test_cast.groovy
index 29691297ef..30530a26da 100644
--- a/regression-test/suites/nereids_p0/datatype/test_cast.groovy
+++ b/regression-test/suites/nereids_p0/datatype/test_cast.groovy
@@ -94,4 +94,23 @@ suite("test_cast") {
         sql "select cast(true as date);"
         result([[null]])
     }
+    sql """ DROP TABLE IF EXISTS table_decimal38_4;"""
+    sql """
+        CREATE TABLE IF NOT EXISTS table_decimal38_4 (
+            `k0` decimal(38, 4)
+        )
+        DISTRIBUTED BY HASH(`k0`) BUCKETS 5 properties("replication_num" = "1");
+        """
+
+    sql """ DROP TABLE IF EXISTS table_decimal27_9;"""
+    sql """
+        CREATE TABLE IF NOT EXISTS table_decimal27_9 (
+            `k0` decimal(27, 9)
+        )
+        DISTRIBUTED BY HASH(`k0`) BUCKETS 5 properties("replication_num" = "1");
+        """
+    explain {
+        sql """select k0 from table_decimal38_4 union all select k0 from table_decimal27_9;"""
+        contains """AS DECIMALV3(38, 4)"""
+    }
 }
\ No newline at end of file