Update fails to update after sub-queries

Question

Hello,
I am trying to run a script which below which will query the product table and then update the sales_info table with the correct ca_product_con description (instead of a code). The problem is I get now rows updated. Can anyone explain whats happening?
query
UPDATE sales_info
SET old_description = ( SELECT ca_product_con.description
FROM ca_product_con
WHERE ca_product_con.old_code = sales_info.old_description)
WHERE EXISTS
  ( SELECT ca_product_con.DESCRIPTION
    FROM ca_product_con
    WHERE ca_product_con.old_code = sales_info.old_description);
sales_info table
OLD_SYSTEM_ID             OLD_DESCRIPTION                     ORDER_DATE                SHIP_DATE                 QUANTITY               TOTAL                 
CA-93301-EM:3490-1        00000916                            27-JAN-99                 01-FEB-99                 7                                            
CA-93301-EM:3490-2        00000916                            27-JAN-99                 01-FEB-99                 1                                            
CA-93301-EM:3498-1        00000926                            07-APR-99                 07-APR-99                 50                                           
CA-93301-EM:3498-2        00000946                            07-APR-99                 07-APR-99                 2         
ca_product_con table
DESCRIPTION                         OLD_CODE       
ACE TENNIS RACKET I                 00000916       
ACE TENNIS RACKET II                00000917       
ACE TENNIS BALLS-3 PACK             00000926       
ACE TENNIS BALLS-6 PACK             00000927       
ACE TENNIS NET                      00000946  Thanks
M

Answer 1

try this .. might be space values are there in both fields if CHAR datatype.
UPDATE sales_info
SET old_description = ( SELECT ca_product_con.description
FROM ca_product_con
WHERE trim(ca_product_con.old_code) = trim(sales_info.old_description) )
WHERE EXISTS
( SELECT ca_product_con.DESCRIPTION
FROM ca_product_con
WHERE trim(ca_product_con.old_code) = trim(sales_info.old_description));