If you have upgraded your MySQL to MySQL 8 version and still using older version of PHP you might encounter a few problems in the connection using mysqli connector library. 1. The first problem we are going to solve is: php mysql 8: "Server sent charset (255) unknown to the client. Please, report to the developers" The problem is that MySQL have changed the default character set from utf8 to utf8mb4 and it is not supported by mysqli connector (nor PDO as I have checked) in older versions of php. "The default collation for utf8mb4 differs between MySQL 5.7 and 8.0 ( utf8mb4_general_ci for 5.7, utf8mb4_0900_ai_ci for 8.0). When the 8.0 client requests a character set of utf8mb4 , what it sends to the server is the default 8.0 utf8mb4 collation; that is, the utf8mb4_0900_ai_ci." https://dev.mysql.com/doc/refman/8.0/en/charset-connection.html The way to solve it easily (there are other ways, such as upgrading php or connectors and more ...) is to force MySQL 8.0 to ...
Points regarding computing that I always forget - so I write them here to find them easily and maybe other could benefit too.