Improve this answer. Apparently the "merge into" statement is not atomic. It can result in "ORA unique constraint" when used concurrently. The check for existence of a match and the insertion of a new record are not protected by a lock, so there is a race condition. To do this reliably, you need to catch this exception and either re-run the merge or do a simple update instead.
In Oracle 10, you can use the "log errors" clause to make it continue with the rest of the rows when an error occurs and log the offending row to another table, rather than just stopping.
Hi, I tried to use same query pattern in my query but somehow my query is inserting duplicate rows. I am not able to find more information about DUAL table. Shekhar Dual is a dummy table with a single row and columnn adp-gmbh. TimSylvester - Oracle uses transactions, so guarantees the snapshot of data at the start of a transaction is consistent throughout the transaction save any changes made within it. So, you'll never have a race condition if a constraint check is done before the insert regardless of how many concurrent calls are made to same SQL code.
Worst case, you may get lots of contention and Oracle will take much longer to reach a final state. RandyMagruder Is it the case that its and we still cannot do a upsert reliably in Oracle! Do you know of a concurrent safe solution? Show 7 more comments. Synesso I've come back here to check out this pattern again. It fails silently when concurrent inserts are attempted.
One insert takes effect, the second merge neither inserts or updates. However, the faster approach of doing two separate statements is safe.
Too bad that with this pattern we need to write twice the data John, Smith NicolasBarbulesco this answer doesn't need to write the data twice: stackoverflow. Tony Andrews Tony Andrews k 20 20 gold badges silver badges bronze badges. The issue is that you have a window in between the insert and the update where another process could successfully fire a delete. I did however use this pattern on a table that never has deletes fired against it. You Asked Dear Team.
Thanks and Regards,. Thank you Chris.. Including role into default role for the user, solved my problem. When we create users with Manage users and groups in oracle apex 5. We'll first look at how to grant and revoke privileges on tables and then how to grant and revoke privileges on functions and procedures in Oracle. You can grant users various privileges to tables. For example:. Sounds pretty similar the problem outlined above, except that merge wants the new records to be in a staging table.
Luckily enough, we can fake a staging table using DUAL:. With the merge statement, we now have a single more complex query instead of the 3 we started with, or the two of the refined approach. However, for the case where inserts are most popular, I believe the merge will perform slightly worse than the code in the Primarily Inserts section, as it still checks if the record exists before attempting to merge it, as the explain plan below shows:.
However, there is a chance that it is better optimized inside Oracle, which leaves an interesting theory to investigate. If exists update else insert A frequent occurrence when writing database procedures is to handle a scenario where given a set of fields, for example a new employee record, update the existing employee record if it exists otherwise create it.
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