Question: I am setting up a database with clients. The use of the dual table allows you to enter your values in a select statement, even though the values are not currently stored in a table. Based on the contacts and customers table, insert into the contacts table all customers who reside in the state of 'Florida'. Since the number of fields in the contacts and customers table are the same and the fields are listed in the same order, you could write the solution as follows though it is generally better practice to list the column names in case the table definitions change :.
Are you expecting more inserts or more updates? The one that is most likely to succeed should go first. If you pick the wrong one you will get a bunch of unnecessary index reads. Not a huge deal but still something to consider. Stack Overflow for Teams — Collaborate and share knowledge with a private group.
Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. Ask Question. Asked 13 years, 2 months ago. Active 6 months ago. Viewed k times. The UPSERT operation either updates or inserts a row in a table, depending if the table already has a row that matches the data: if table t has a row exists that has key X: update t set mystuff Mark Harrison Mark Harrison k gold badges silver badges bronze badges.
Add a comment. Active Oldest Votes. 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.
Hi Tom, I am really interested in knowing how to improve the performance of merge. I need to usually merge about a million records. It takes lot of time. Regards, HH. October 21, - am UTC. Merge would not - merge would alert you to the ambiguity. I'm not a fan of the "view does automagic trickery in the background" approach. As you can not create an Index on an external table the MERGE must look at the source tables PK for every single row in the external table because its not sorted.
Regards Wolfgang. October 21, - pm UTC. I would hope for two full scans and an hash outer join. As I read your books, I would have thought the same We will implement this the next months. We don't load only one table but about Perhaps it would be better to split the file delivered from the mainfraim into smaller pieces, so that we don't have to fullscan a 10 million rows table for just Inserts.
As far it's not possible to create stats at an external table? Am I right? That leeds to another question: How does the CBO know how many rows we might have in the external table? Is Oracle aware of the filesize? If you're interested in, I will poste our procedure how we solved it.
But it will take a few month They have prevented me to believe some Oracle gurus like Donald B.
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