From e921d4ea32cc7224f8898b76f7576652188e97cb Mon Sep 17 00:00:00 2001
From: Minh Vu <vuhoangminh97@gmail.com>
Date: Mon, 24 Aug 2026 15:04:02 +0200
Subject: [PATCH 1/2] Validate Decimal parameters before swapping

---
 clickhouse/columns/decimal.cpp | 13 +++++++++++
 ut/columns_ut.cpp              | 40 ++++++++++++++++++++++++++++++++++
 2 files changed, 53 insertions(+)

diff --git a/clickhouse/columns/decimal.cpp b/clickhouse/columns/decimal.cpp
index 30c4f9f1..cda00a71 100644
--- a/clickhouse/columns/decimal.cpp
+++ b/clickhouse/columns/decimal.cpp
@@ -236,6 +236,19 @@ ColumnRef ColumnDecimal::CloneEmpty() const {
 
 void ColumnDecimal::Swap(Column& other) {
     auto & col = dynamic_cast<ColumnDecimal &>(other);
+
+    if (col.GetPrecision() != GetPrecision()) {
+        throw ValidationError("Can't swap Decimal columns when precisions are not the same: "
+            + std::to_string(GetPrecision()) + "(this) != "
+            + std::to_string(col.GetPrecision()) + "(that)");
+    }
+
+    if (col.GetScale() != GetScale()) {
+        throw ValidationError("Can't swap Decimal columns when scales are not the same: "
+            + std::to_string(GetScale()) + "(this) != "
+            + std::to_string(col.GetScale()) + "(that)");
+    }
+
     data_.swap(col.data_);
 }
 
diff --git a/ut/columns_ut.cpp b/ut/columns_ut.cpp
index 8421b5d2..d1b30bba 100644
--- a/ut/columns_ut.cpp
+++ b/ut/columns_ut.cpp
@@ -184,6 +184,46 @@ TEST(ColumnsCase, DecimalStringAt) {
 
 }
 
+TEST(ColumnsCase, DecimalSwap) {
+    auto column1 = std::make_shared<ColumnDecimal>(18, 2);
+    auto column2 = std::make_shared<ColumnDecimal>(18, 2);
+    column1->Append("1.23");
+    column2->Append("4.56");
+
+    column1->Swap(*column2);
+
+    EXPECT_EQ(column1->StringAt(0), "4.56");
+    EXPECT_EQ(column2->StringAt(0), "1.23");
+}
+
+TEST(ColumnsCase, DecimalSwapDifferentScale) {
+    auto column1 = std::make_shared<ColumnDecimal>(18, 2);
+    auto column2 = std::make_shared<ColumnDecimal>(18, 3);
+    column1->Append("1.23");
+    column2->Append("4.567");
+
+    EXPECT_THROW(column1->Swap(*column2), ValidationError);
+
+    EXPECT_EQ(column1->GetType().GetName(), "Decimal(18,2)");
+    EXPECT_EQ(column2->GetType().GetName(), "Decimal(18,3)");
+    EXPECT_EQ(column1->StringAt(0), "1.23");
+    EXPECT_EQ(column2->StringAt(0), "4.567");
+}
+
+TEST(ColumnsCase, DecimalSwapDifferentPrecision) {
+    auto column1 = std::make_shared<ColumnDecimal>(9, 2);
+    auto column2 = std::make_shared<ColumnDecimal>(18, 2);
+    column1->Append("1.23");
+    column2->Append("4.56");
+
+    EXPECT_THROW(column1->Swap(*column2), ValidationError);
+
+    EXPECT_EQ(column1->GetType().GetName(), "Decimal(9,2)");
+    EXPECT_EQ(column2->GetType().GetName(), "Decimal(18,2)");
+    EXPECT_EQ(column1->StringAt(0), "1.23");
+    EXPECT_EQ(column2->StringAt(0), "4.56");
+}
+
 TEST(ColumnsCase, NumericInit) {
     auto col = std::make_shared<ColumnUInt32>(MakeNumbers());
 

From 7dc75acd33e9a2b183b5e2b628ef8f09b341945b Mon Sep 17 00:00:00 2001
From: Minh Vu <vuhoangminh97@gmail.com>
Date: Mon, 24 Aug 2026 15:23:49 +0200
Subject: [PATCH 2/2] Test Decimal precision mismatch with same storage type

---
 ut/columns_ut.cpp | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/ut/columns_ut.cpp b/ut/columns_ut.cpp
index d1b30bba..1eaaf64e 100644
--- a/ut/columns_ut.cpp
+++ b/ut/columns_ut.cpp
@@ -224,6 +224,20 @@ TEST(ColumnsCase, DecimalSwapDifferentPrecision) {
     EXPECT_EQ(column2->StringAt(0), "4.56");
 }
 
+TEST(ColumnsCase, DecimalSwapDifferentPrecisionSameStorageType) {
+    auto column1 = std::make_shared<ColumnDecimal>(17, 2);
+    auto column2 = std::make_shared<ColumnDecimal>(18, 2);
+    column1->Append("1.23");
+    column2->Append("4.56");
+
+    EXPECT_THROW(column1->Swap(*column2), ValidationError);
+
+    EXPECT_EQ(column1->GetType().GetName(), "Decimal(17,2)");
+    EXPECT_EQ(column2->GetType().GetName(), "Decimal(18,2)");
+    EXPECT_EQ(column1->StringAt(0), "1.23");
+    EXPECT_EQ(column2->StringAt(0), "4.56");
+}
+
 TEST(ColumnsCase, NumericInit) {
     auto col = std::make_shared<ColumnUInt32>(MakeNumbers());