Dynamic columns allows you to store a different set of columns for every row in the table. […]
Dynamic columns works by storing the extra columns in a blob and having a small set of functions to manipulate it. The functions exist both in SQL and in the MariaDB client library to allow you to manipulate the data where it suits you best.
Nice addition to MariaDB that will hopefully make it to MySQL in the future. You can select, add, update and filter on a dynamic column (nb: though I couldn’t find if you can define indexes on dynamic columns or filtering will require full table scans). The only drawback I see at the current implementation is that dynamic columns are positional not named.
Original title and link: Dynamic Columns in MariaDB: a SQL to NoSQL Bridge (NoSQL databases © myNoSQL)