Specifies the columns in a cursor that you or your program might
    later modify with an UPDATE statement. The column names in the
    FOR UPDATE clause must belong to a table or view named in the
    FROM clause.

    You do not have to specify the FOR UPDATE clause of the DECLARE
    CURSOR statement to later modify rows using the UPDATE statement:

    o  If you do specify a FOR UPDATE clause and later specify
       columns in the UPDATE statement that are not in the FOR UPDATE
       clause, SQL issues a warning message and proceeds with the
       update modifications.

    o  If you do not specify a FOR UPDATE clause, you can update
       any column using the UPDATE statement. SQL does not issue any
       messages.

    The FOR UPDATE OF clause in a SELECT statement provides UPDATE
    ONLY CURSOR semantics by locking all the rows selected.