In Oracle, the NVL function allows you to replace NULL with the specified expression i.e. it returns the first operand if it is not NULL, otherwise it returns the second operand.
In MySQL you have to use IFNULL function.
Oracle:
-- Replace NULL SELECT NVL('John', 'N/A') FROM dual; # John -- Replace NULL SELECT NVL(NULL, 'N/A') FROM dual; # N/A
MySQL:
-- Replace NULL SELECT IFNULL('John', 'N/A'); # John -- Replace NULL SELECT IFNULL(NULL, 'N/A'); # N/A
For more information, see Oracle to MySQL Migration.