how to update portion of the varchar type data

I have a table called OBJTABLE with two columns,

   ID number(10)
   OBJECTCODE VARCHAR(200) and I would like to update a portion of the OBJECTCODE field

e.g. one row in the OBJECTCODE column value is '00A BCD'
and I like to update col 4-6 with a value

But when I execute the following SQL I got ORA-00927 MIISSIING EQUAL SIGN

Update OBJTABLE set substr(OBJECTCODE,4,3) = '123' where substr(OBJECTCODE,1,3) = '00A'

I am using Oracle8i.

Have anyone come across a way to update portion of the varchar data type? Thanks in advance for your help! Received on Wed Nov 27 2002 - 20:24:54 CST