I switched from the mariadb client lib to boost::mysql and everything is working fine

Thus, the server definitly sends the data !

The client is also checked to be able receive that data because it does with an older server

In boost::mysql i need to set conn->set_meta_mode(mysql::metadata_mode::full);

There might be a similar problem with defaults and switches in mariadb, although the boost switch does not affect only the data type but column names as well...

thanks for all hints. I will try to find the switch or just keep boost