Updating a table in oracle
As noted earlier, flashback query timestamps are mapped to SCNs, but only once every five minutes.This makes flashback queries with timestamps subject to precision errors.Flashback query enables us to query the undo segments directly, either by SCN (System Change Number) or by timestamp.The means and ease of doing this changed dramatically between Oracle 9.0 and 9.2 and we shall examine both of them in this article.
Note that the initial ALTER SESSION is simply a convenience to enable a consistent timestamp format mask without having to supply it explicitly. The extended FROM clause is simple and intuitive to use and is more likely to encourage developers to use flashback query.This short article introduces flashback query, a new feature of Oracle 9i.Flashback query enables us to query our data as it existed in a previous state.Oracle 9i Release 2 makes flashback query significantly easier by building the capability into the SQL FROM clause itself.
In 9.2, we can query our data AS OF TIMESTAMP or AS OF SCN directly.
In fact, the term "rollback segments" is confined to history (or applies only to manual undo management at least).