COALESCE or IFNULL or VALUE

Returns the first argument that is not null. All arguments must be compatible. IFNULL requires two arguments. COALESCE and VALUE can have any number, two or greater.

Example:

When selecting all the values from all the rows in the DEPARTMENT table, if the department manager (MGRNO) is missing (that is, null), then return a value of 'ABSENT'.

  SELECT DEPTNO, DEPTNAME, COALESCE(MGRNO, 'ABSENT'), ADMRDEPT
    FROM DEPARTMENT