db2 v9.1更新数据报错

表结构如下：create table cbankinterest
(
    workdate   varchar(8)       not null,
    bankid       varchar(12)     not null,
    product     decimal(15,2)  default 0.00  not null,
    interrest_rates   decimal(15,2) default 0.000000 not null,
    interest     decimal(15,2)
);
create unique index cbankinterest_idx1 on cbankinterest (workdate,bankid);

执行update cbankinterest set bankid='235013053027' where bankid='133013051003'
DB20134E  The command was processed as an SQL statement because it was not a
valid Command Line Processor command .During SQL processing it returned:
SQL0803N One or more values in the INSER statement ,UPDATE statement ,or
foreign key update caused by a DELETE statement are not valid because the
table "IDDS.CBANKINTEREST" from having duplicate values for the index key.
SQLSTATE=23505
求助此问题如何处理