Fix "There is no supertype" error on ALTER UPDATE #7306

src/Interpreters/MutationsInterpreter.cpp

@@ -367,15 +367,28 @@ ASTPtr MutationsInterpreter::prepare(bool dry_run)
                         affected_materialized.emplace(mat_column);
                 }
 
-                /// Just to be sure, that we don't change type
+                /// When doing UPDATE column = expression WHERE condition
-                /// after update expression execution.
+                /// we will replace column to the result of the following expression:
+                ///
+                /// CAST(if(condition, CAST(expression, type), column), type)
+                ///
+                /// Inner CAST is needed to make 'if' work when branches have no common type,
+                /// example: type is UInt64, UPDATE x = -1 or UPDATE x = x - 1.
+                ///
+                /// Outer CAST is added just in case if we don't trust the returning type of 'if'.
+
+                auto type_literal = std::make_shared<ASTLiteral>(columns_desc.getPhysical(column).type->getName());
+
                 const auto & update_expr = kv.second;
                 auto updated_column = makeASTFunction("CAST",
                     makeASTFunction("if",
                         command.predicate->clone(),
-                        update_expr->clone(),
+                        makeASTFunction("CAST",
+                            update_expr->clone(),
+                            type_literal),
                         std::make_shared<ASTIdentifier>(column)),
-                    std::make_shared<ASTLiteral>(columns_desc.getPhysical(column).type->getName()));
+                    type_literal);
+
                 stages.back().column_to_updated.emplace(column, updated_column);
             }
 

tests/queries/0_stateless/01413_alter_update_supertype.reference

@@ -0,0 +1,21 @@
+0
+1
+2
+3
+4
+5
+6
+7
+8
+9
+---
+0
+0
+2
+2
+4
+4
+6
+6
+8
+8

tests/queries/0_stateless/01413_alter_update_supertype.sql

@@ -0,0 +1,13 @@
+DROP TABLE IF EXISTS t;
+CREATE TABLE t (x UInt64) ENGINE = MergeTree ORDER BY tuple();
+INSERT INTO t SELECT number FROM numbers(10);
+
+SELECT * FROM t;
+
+SET mutations_sync = 1;
+ALTER TABLE t UPDATE x = x - 1 WHERE x % 2 = 1;
+
+SELECT '---';
+SELECT * FROM t;
+
+DROP TABLE t;