Detect updated records

Question

Hi all,
is there a way to find all the updated record of a table?
(I don't have any field on the table that can help me such as update_date or similar).
Thanks.

Answer 1

I don't think we're disagreeing, just want to make sure I'm following
rp0428 wrote:
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If there was a timestamp on the row, your refresh process would need to know the timestamp that the destination was current as of and would need to pull the changes since that timestamp.
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Unfortunately that approach has a big, gaping hole which can render it unreliable.True. But using a timestamp to do the replication was never a suggestion here. Dan correctly pointed out that if you wanted to convert the SCN to a timestamp, there are limits on the accuracy of the conversion and the time frame during which that conversion is possible. I was simply emphasizing that there was no need to do that conversion in the first place unless you needed to know when a row changed rather than merely that it had changed and I compared how you would identify changed data using the ORA_ROWSCNto how you might do it if there was a timestamp that could be used.
The value of the timestamp is typically set by using SYSDATE or SYSTIMESTAMP but the record containing that value isn't 'current' until the record is committed.
So if a query/process begins before midnight tonight but is not commited until after midnight (e.g. 1am tomorrow) the timestamp will have today's value but will NOT get pulled by a query after midnight but before 1am and processed in tonight's batch process.
That data will also not get processed in tomorrow's batch process because the timestamp makes it appear as if it has already been processed.
Timestamp's only work reliably when it is known that the above use case cannot happen.Or if you define a maximum transaction length and pull data since last_extract_time - maximum_transaction_length. Obviously not perfect, which is why there are tons of technologies to allow you to replicate changes (CDC, Streams, materialized views, etc.) rather than rolling your own solution. Using the SCN would, of course, be preferrable from a correctness standpoint in the extremely rare case that there is a need to roll your own change data capture process.
Justin