The generation-expression cannot contain any of the following (SQLSTATE 42621):

    *  Subqueries 
    * XMLQUERY or XMLEXISTS expressions
    * Column functions
    * Dereference operations or DEREF functions
    * User-defined or built-in functions that are non-deterministic
    * User-defined functions using the EXTERNAL ACTION option
    * User-defined functions that are not defined with NO SQL
    * Host variables or parameter markers
    * Special registers and built-in functions that depend on the value of a special register
    * Global variables
    * References to columns defined later in the column list
    * References to other generated columns
    * References to columns of type XML