HOW UPDATE INTERNAL WORKS

Hi,
My question is related to the architecture. I don't find much information on google.
The question is how Oracle update statement works on the background? My friend and myself had a debate that update works internally as delete and insert statements. It means when you run update, first it deletes the row and insert the row with new update values.
But I don't agree his view on this.
Can anyone of you clarify how oracle update statement works internally? Thanks in advance..
Regards,
Robin

>
It means when you run update, first it deletes the row and insert the row with new update values.
But I don't agree his view on this.
>
But you didn't say what your view is!
Generally speaking this doesn't happen unless the ROWID is changing. This can happen for an update of the partition key of a partitioned table that moves the row to a different partition (and maybe even a different tablespace and file. For that case Oracle WILL delete the record and reinsert it in the new location.
Rows are stored in row pieces. So when a row is updated then one or more pieces have to be updated. Depending on which row piece is affected and what, if anything is in the block after that row piece the row piece may need to be moved (rewritten) to another location in the block or even to another block.
See How Table Data Is Stored in the Database Concepts doc
http://docs.oracle.com/cd/B28359_01/server.111/b28318/schema.htm

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