From d8e670297bcdc1850260a1d60d4ee39b2a895a4d Mon Sep 17 00:00:00 2001
From: Yarik Briukhovetskyi <114298166+yariks5s@users.noreply.github.com>
Date: Tue, 10 Sep 2024 17:42:27 +0200
Subject: [PATCH] groupConcat consistency

---
 .../AggregateFunctionGroupConcat.cpp                | 13 +++++++++++--
 .../03235_groupArray_returns_string.reference       |  1 +
 .../0_stateless/03235_groupArray_returns_string.sql | 10 ++++++++++
 3 files changed, 22 insertions(+), 2 deletions(-)
 create mode 100644 tests/queries/0_stateless/03235_groupArray_returns_string.reference
 create mode 100644 tests/queries/0_stateless/03235_groupArray_returns_string.sql

diff --git a/src/AggregateFunctions/AggregateFunctionGroupConcat.cpp b/src/AggregateFunctions/AggregateFunctionGroupConcat.cpp
index 636ac80e350..8fb0b645096 100644
--- a/src/AggregateFunctions/AggregateFunctionGroupConcat.cpp
+++ b/src/AggregateFunctions/AggregateFunctionGroupConcat.cpp
@@ -116,15 +116,17 @@ class GroupConcatImpl final
     SerializationPtr serialization;
     UInt64 limit;
     const String delimiter;
+    const DataTypePtr type;
 
 public:
     GroupConcatImpl(const DataTypePtr & data_type_, const Array & parameters_, UInt64 limit_, const String & delimiter_)
         : IAggregateFunctionDataHelper<GroupConcatData<has_limit>, GroupConcatImpl<has_limit>>(
             {data_type_}, parameters_, std::make_shared<DataTypeString>())
-        , serialization(this->argument_types[0]->getDefaultSerialization())
         , limit(limit_)
         , delimiter(delimiter_)
+        , type(data_type_)
     {
+        serialization = isFixedString(type) ? std::make_shared<DataTypeString>()->getDefaultSerialization() : this->argument_types[0]->getDefaultSerialization();
     }
 
     String getName() const override { return name; }
@@ -140,7 +142,14 @@ public:
         if (cur_data.data_size != 0)
             cur_data.insertChar(delimiter.c_str(), delimiter.size(), arena);
 
-        cur_data.insert(columns[0], serialization, row_num, arena);
+        if (isFixedString(type))
+        {
+            ColumnWithTypeAndName col = {columns[0]->getPtr(), type, "column"};
+            const auto & col_str = castColumn(col, std::make_shared<DataTypeString>());
+            cur_data.insert(col_str.get(), serialization, row_num, arena);
+        }
+        else
+            cur_data.insert(columns[0], serialization, row_num, arena);
     }
 
     void merge(AggregateDataPtr __restrict place, ConstAggregateDataPtr rhs, Arena * arena) const override
diff --git a/tests/queries/0_stateless/03235_groupArray_returns_string.reference b/tests/queries/0_stateless/03235_groupArray_returns_string.reference
new file mode 100644
index 00000000000..d00491fd7e5
--- /dev/null
+++ b/tests/queries/0_stateless/03235_groupArray_returns_string.reference
@@ -0,0 +1 @@
+1
diff --git a/tests/queries/0_stateless/03235_groupArray_returns_string.sql b/tests/queries/0_stateless/03235_groupArray_returns_string.sql
new file mode 100644
index 00000000000..618ec6f839b
--- /dev/null
+++ b/tests/queries/0_stateless/03235_groupArray_returns_string.sql
@@ -0,0 +1,10 @@
+CREATE TABLE t (st FixedString(54)) ENGINE=MergeTree ORDER BY ();
+
+INSERT INTO t VALUES 
+('abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRTUVWXYZ'),
+('\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0'),
+('IIIIIIIIII\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0');
+
+WITH (SELECT groupConcat(',')(st) FROM t) AS a,
+     (SELECT groupConcat(',')(st :: String) FROM t) AS b
+SELECT equals(a, b);