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 SELECT
    statement to later modify rows using the UPDATE statement:

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

    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.