From e243969519781def3321583a1376e1de623bbeb0 Mon Sep 17 00:00:00 2001
From: Andrey Zvonov <32552679+zvonand@users.noreply.github.com>
Date: Fri, 10 Jul 2026 20:25:14 +0200
Subject: [PATCH] Merge pull request #1994 from Altinity/backport/25.8/93814

Backport of #93814 to 25.8: Fix logical error in `Map` column types when used with empty tuple
---
 src/Functions/array/array.cpp                 |  3 +-
 .../03786_empty_tuple_map_array.reference     |  4 ++
 .../03786_empty_tuple_map_array.sql           | 43 +++++++++++++++++++
 3 files changed, 49 insertions(+), 1 deletion(-)
 create mode 100644 tests/queries/0_stateless/03786_empty_tuple_map_array.reference
 create mode 100644 tests/queries/0_stateless/03786_empty_tuple_map_array.sql

diff --git a/src/Functions/array/array.cpp b/src/Functions/array/array.cpp
index 715ee70bf9b8..15b75c5f7bbf 100644
--- a/src/Functions/array/array.cpp
+++ b/src/Functions/array/array.cpp
@@ -253,7 +253,8 @@ class FunctionArray : public IFunction
         const size_t tuple_size = concrete_out_data->tupleSize();
         if (tuple_size == 0)
         {
-            out_data.insertManyDefaults(columns.size());
+            /// Tuple() has no subcolumns to fill. Create `columns.size()` elements per row to match array offsets
+            out_data.insertManyDefaults(columns.size() * input_rows_count);
         }
         else
         {
diff --git a/tests/queries/0_stateless/03786_empty_tuple_map_array.reference b/tests/queries/0_stateless/03786_empty_tuple_map_array.reference
new file mode 100644
index 000000000000..590860f31966
--- /dev/null
+++ b/tests/queries/0_stateless/03786_empty_tuple_map_array.reference
@@ -0,0 +1,4 @@
+{((),1):1,((),1):1}
+{((),1):1,((),1):1}
+{}
+{((),1):1,((),1):1}
diff --git a/tests/queries/0_stateless/03786_empty_tuple_map_array.sql b/tests/queries/0_stateless/03786_empty_tuple_map_array.sql
new file mode 100644
index 000000000000..5d6cce952c96
--- /dev/null
+++ b/tests/queries/0_stateless/03786_empty_tuple_map_array.sql
@@ -0,0 +1,43 @@
+DROP TABLE IF EXISTS t0;
+
+CREATE TABLE t0 (c0 Map(Tuple(Tuple(), Int), Int))
+ENGINE = MergeTree()
+ORDER BY tuple();
+
+INSERT INTO TABLE t0 (c0)
+VALUES
+(
+    map(
+        ((), 1), 1,
+        ((), 1), 1
+    )
+),
+(
+    map(
+        ((), 1), 1,
+        ((), 1), 1
+    )
+);
+
+SELECT * FROM t0;
+
+
+DROP TABLE IF EXISTS t1;
+
+CREATE TABLE t1 (c0 Map(Tuple(Tuple(), Int), Int))
+ENGINE = MergeTree()
+ORDER BY tuple();
+
+INSERT INTO TABLE t1 (c0)
+VALUES
+(
+    map()
+),
+(
+    map(
+        ((), 1), 1,
+        ((), 1), 1
+    )
+);
+
+SELECT * FROM t1;