Question regarding FOR UPDATE

[Martin Neumann]

Hello,

I'm trying to run following SQL query:
SELECT
    ID,
    BROKER_NAME AS B,
    CSV_REG_EX AS C,
    ACTIVE
FROM
    APP.BROKERS
FOR UPDATE OF
    B,
    C,
    ACTIVE;

and get this error.

[Exception, Error code 30,000, SQLState 42X04] Column 'B' is either not 
in any table in the FROM list or appears within a join specification and 
is outside the scope of the join specification or appears in a HAVING 
clause and is not in the GROUP BY list. If this is a CREATE or ALTER 
TABLE  statement then 'B' is not a column in the target table.
  Line 1, column 1


Derby 10.15.1.3 is running on openJDK12 within Netbeans 11.0.

When I remove the alias for BROKER_NAME AND CVS_REG_EX it works.

Reading the documentation my understanding is that FOR UPDATE should 
also work with aliased columns.

Any advise is appreciated.

Thanks and best regards
Martin