Migrating a Sybase Index with ignore_dup_key

Question

HI All,
I am involved with Sybase to Oracle migration.
I need to migrate a Index with ignore_dup_key.
I am currently inserting the data into the table and then deleting the duplicate enteries.
Can someone suggest me a better approach..
Thanks,
Riddhisha
Edited by: Riddhisha on Apr 13, 2012 3:18 PM

Answer 1

I think there is some confusion around ignore_dup_key functionality. Ignore_dup_key in Sybase essentially allows an application to continue without aborting a on-going transaction even if there was an attempt to insert duplicate values for columns that have a Unique index on them with ignore_dup_key clause. But (I emphasize) Sybase does not allow duplicate values in a column on which a unique index exists.
Typically when you try to insert duplicate values for columns with unique/primary indexes, you get a "unique constraint violation error". This error under normal conditions will result in the failure of the complete transaction. With IGNORE_DUP_KEY clause, the sybase database simply ignores that "INSERT/UPDATE" statement and continues with the rest of the transaction.
What that means is if you have a index on a table in Sybase with Ignore_dup_key clause then most likely that index is a UNIQUE index. So that means you shouldn't see duplicate values in the affected column(s). If you do see duplicate values then the implication is that the index is not a UNIQUE index and hence IGNORE_DUP_KEY clause does not really add value. Customer may have changed their schema design later realizing that those columns will have duplicate values but forgot to take out the IGNORE_DUP_KEY clause. Also if you already have duplicate values for a column, you cannot create a UNIQUE index even in Sybase with this clause.
Since you are seeing duplicate values in the table so I am guessing that it is a regular B*tree index so you can do the same in Oracle and ignore the IGNORE_DUP_KEY clause as Oracle does not offer such functionality.
If you really want to create a unique index in Oracle and not have the duplicate values then you will have to try couple of different approaches. Create an External table and use PL/SQL procedure/function to load the data using MERGE statements or INSERT INTO... SELECT FROM EXTERNAL_TABLE with the LOG ERROR Clause to reject the duplicate values without failing the overall data load.
Hope this helps..
Regards
Prakash