When I used ClickHouse's MaterializeMySQL feature to synchronize data from MySQL to ClickHouse, I had some problems. The Click House version I'm using is 20.10.3.30, and the MySQL version I'm using is 5.7.28-log.

The SQL statement I executed is as follows:
> SET allow_experimental_database_materialize_mysql = 1;
drop database if exists ck_test;
CREATE DATABASE if not exists ck_test ENGINE = MaterializeMySQL('x.x.x.x:3306', 'test', 'user', 'test');


After I executed the SQL statement, I saw the following information from the error log /var/log/clickhouse-server/clickhouse-server.err. Log:

> 2020.11.10 20:27:39.611578 [ 33057 ] {} <Error> MaterializeMySQLSyncThread: Code: 20, e.displayText() = DB::Exception: mysqlxx::UseQueryResult contains 4 columns while 2 expected, Stack trace (when copying this message, always include the lines below):

> 0. DB::MySQLBlockInputStream::MySQLBlockInputStream(mysqlxx::Pool::Entry const&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, DB::Block const&, unsigned long, bool) @ 0xe587457 in /usr/bin/clickhouse

> 1. DB::MaterializeMetadata::MaterializeMetadata(mysqlxx::Pool::Entry&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, bool&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&) @ 0xdb1cbf3 in /usr/bin/clickhouse

> 2. DB::MaterializeMySQLSyncThread::prepareSynchronized(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&) @ 0xdaf8bf1 in /usr/bin/clickhouse

> 3. DB::MaterializeMySQLSyncThread::synchronization(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&) @ 0xdaf836a in /usr/bin/clickhouse

> 4. ? @ 0xdb1480d in /usr/bin/clickhouse

> 5. ThreadPoolImpl<std::__1::thread>::worker(std::__1::__list_iterator<std::__1::thread, void*>) @ 0x7b8963d in /usr/bin/clickhouse

> 6. ? @ 0x7b8d153 in /usr/bin/clickhouse

> 7. start_thread @ 0x7dd5 in /usr/lib64/libpthread-2.17.so

> 8. __clone @ 0xfdead in /usr/lib64/libc-2.17.so

>  (version 20.10.3.30 (official build))


Does anybody have a problem like this?
const int ER_BAD_DB_ERROR = 1049;
    struct Buffers
    {
        String database;
        
        size_t max_block_rows = 0;
        size_t max_block_bytes = 0;
        size_t total_blocks_rows = 0;
        size_t total_blocks_bytes = 0;
        using BufferAndSortingColumns = std::pair<Block, std::vector<size_t>>;
        using BufferAndSortingColumnsPtr = std::shared_ptr<BufferAndSortingColumns>;
        std::unordered_map<String, BufferAndSortingColumnsPtr> data;
        Buffers(const String & database_) : database(database_) {}
        void commit(const Context & context);
        void add(size_t block_rows, size_t block_bytes, size_t written_rows, size_t written_bytes);
        bool checkThresholds(size_t check_block_rows, size_t check_block_bytes, size_t check_total_rows, size_t check_total_bytes) const;
        BufferAndSortingColumnsPtr getTableDataBuffer(const String & table, const Context & context);
    };
    void synchronization(const String & mysql_version);
    bool isCancelled() { return sync_quit.load(std::memory_order_relaxed); }
    std::optional<MaterializeMetadata> prepareSynchronized(const String & mysql_version);
    void flushBuffersData(Buffers & buffers, MaterializeMetadata & metadata);
    void onEvent(Buffers & buffers, const MySQLReplication::BinlogEventPtr & event, MaterializeMetadata & metadata);
    std::atomic<bool> sync_quit{false};
    std::unique_ptr<ThreadFromGlobalPool> background_thread_pool;
    void executeDDLAtomic(const QueryEvent & query_event);
};
}
#endif