Backport #71679 to 24.9: Fix LOGICAL_ERROR when doing ALTER with empty tuple

src/Functions/FunctionsComparison.h

@@ -1048,6 +1048,9 @@ private:
             size_t tuple_size,
             size_t input_rows_count) const
     {
+        if (0 == tuple_size)
+            throw Exception(ErrorCodes::NOT_IMPLEMENTED, "Comparison of zero-sized tuples is not implemented");
+
         ColumnsWithTypeAndName less_columns(tuple_size);
         ColumnsWithTypeAndName equal_columns(tuple_size - 1);
         ColumnsWithTypeAndName tmp_columns(2);

src/Functions/if.cpp

@@ -668,6 +668,9 @@ private:
         temporary_columns[0] = arguments[0];
 
         size_t tuple_size = type1.getElements().size();
+        if (tuple_size == 0)
+            return ColumnTuple::create(input_rows_count);
+
         Columns tuple_columns(tuple_size);
 
         for (size_t i = 0; i < tuple_size; ++i)

tests/queries/0_stateless/03268_empty_tuple_update.reference

@@ -0,0 +1 @@
+()	2

tests/queries/0_stateless/03268_empty_tuple_update.sql

@@ -0,0 +1,11 @@
+DROP TABLE IF EXISTS t0;
+
+CREATE TABLE t0 (c0 Tuple(), c1 int) ENGINE = Memory();
+
+INSERT INTO t0 VALUES ((), 1);
+
+ALTER TABLE t0 UPDATE c0 = (), c1 = 2 WHERE EXISTS (SELECT 1);
+
+SELECT * FROM t0;
+
+DROP TABLE t0;