Oracle 10g update table i from table 2 column join error - sql

Question

I have the following Oracle 10g sql which to me looks about right:
update ( select OLD1.TC_CUSTOMER_NUMBER,NEW1.PRD_CUST_NUMBER
FROM TBYC84_PROFILE_ACCOUNT OLD1,
TMP_PRD_KEP NEW1
WHERE
OLD1.TC_CUSTOMER_NUMBER = NEW1.KEP_CUST_NUMBER )
SET
TC_CUSTOMER_NUMBER = PRD_CUST_NUMBER
But i am getting this error when i run the script:
SQL Error: ORA-01779: cannot modify a column which maps to a non key-preserved table
01779. 00000 - "cannot modify a column which maps to a non key-preserved table"
*Cause: An attempt was made to insert or update columns of a join view which
map to a non-key-preserved table.
*Action: Modify the underlying base tables directly.
I have done done some research on this error but not quite sure how to remedy.
So my question is, how can i fix this or is there a better way to write the update sql?
Any help would be appreciated.
many thanks
UPDATE
I have changed the update sql to this:
update
TBYC84_PROFILE_ACCOUNT PA
set
(
PA.TC_CUSTOMER_NUMBER
) = (
select
TPK.PRD_CUST_NUMBER
from
TMP_PRD_KEP TPK
where
TPK.KEP_CUST_NUMBER = PA.TC_CUSTOMER_NUMBER
)
Now this has updated the TBYC84_PROFILE_ACCOUNT table AND nulled out the TC_CUSTOMER_NUMBER
column.
Why did it do this?
There may be more than one row in the TBYC84_PROFILE_ACCOUNT.TC_CUSTOMER_NUMBER
that has the same account number but for different user_id's.
Please can anyone assist in helping me resolve this.
All I need to to is update the TBYC84_PROFILE_ACCOUNT.TC_CUSTOMER_NUMBER to the one that is xrefed in the TMP_PRD_KEP, surely this is not impossible.
many thanks

Answer 1

For an UPDATE statement, all the columns that are updated must be extracted from a key-preserved table.
Also:
A key-preserved table is one for which every primary key or unique key value in the base table is also unique in the join view.
Here.
In this case, TBYC84_PROFILE_ACCOUNT is being updated. So, it must be key-preserved in the view's subquery. Currently it is not. It must be changed in a way that it becomes key-preserved by involving primary or unique columns in the where clause. If not possible, you should try to update the base table instead.
UPDATE
In case of the table update problem, assuming the subquery returns at most one distinct value for the TC_CUSTOMER_NUMBER column, the reason you get NULLs is that all records are being updated even if they do not have any matching records in the TMP_PRD_KEP table. So, the parent update statement needs to be fitted with a where clause:
update
TBYC84_PROFILE_ACCOUNT PA
set
(
PA.TC_CUSTOMER_NUMBER
) = (
select
TPK.PRD_CUST_NUMBER
from
TMP_PRD_KEP TPK
where
TPK.KEP_CUST_NUMBER = PA.TC_CUSTOMER_NUMBER
)
where exists(select *
from TMP_PRD_KEP TPK
where TPK.KEP_CUST_NUMBER = PA.TC_CUSTOMER_NUMBER)
;

Answer 2

Create a index on the columns used in your where clause predicates. That should solve your problem.