In Oracle, the NVL function allows you to replace NULL with the specified expression: it returns the first operand if it is not NULL, and the second operand otherwise.
MariaDB also provides the NVL function (since 10.3.1) in both native and Oracle compatibility modes.
Oracle:
-- Replace NULL SELECT NVL('John', 'N/A') FROM dual; /* John */ -- Replace NULL SELECT NVL(NULL, 'N/A') FROM dual; /* N/A */
MariaDB - Oracle Compatibility:
-- Replace NULL SELECT NVL('John', 'N/A'); /* John */ -- Replace NULL SELECT NVL(NULL, 'N/A'); /* N/A */
For more information, see Oracle to MariaDB Migration - Oracle Compatibility Mode.