If you invoke multiple databases in the RDO interface and declare an
    aggregate expression, Oracle Rdb returns an %RDB-E-INVALID_BLR error.
    For example:

    RDO> INVOKE DATABASE FEE = FILENAME USER1:[STUDENT_FEES]STUDENTDB
    RDO> INVOKE DATABASE STA = FILENAME USER2:[STUDENT_FEES]STATS
    RDO>
    RDO> START_TRANSACTION ON FEE USING
    cont>   (READ_ONLY RESERVING FEE.TRANS FOR SHARED READ) AND
    cont>    ON STA USING (READ_WRITE RESERVING STA.STATDATA FOR
    cont>    EXCLUSIVE WRITE)
    RDO>
    RDO>   FOR TX IN FEE.TRANS SORTED BY TX.SNO, TX.SESS, TX.TYPE
    cont>          REDUCED TO TX.SNO, TX.SESS, TX.TYPE
    cont>        WITH TX.SESS = "91S"
    cont>     STORE SX IN STA.STATDATA USING
    cont>        SX.SNO = TX.SNO;
    cont>        SX.SESS = TX.SESS;
    cont>        SX.TYPE = TX.TYPE;
    cont>        SX.AMOUNT = (TOTAL T1.AMOUNT OF T1 IN FEE.TRANS WITH
    cont>           T1.SNO = TX.SNO AND
    cont>           T1.SESS = TX.SESS AND
    cont>           T1.TYPE = TX.TYPE);
    cont>     END_STORE
    cont>  END_FOR
    %RDB-E-INVALID_BLR, request BLR is incorrect at offset 172
    RDO> ROLLBACK;