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ORA_ROWSCN Pseudocolumn

ORA_ROWSCN reflects the system change-number (SCN) of the most recent change to a row. This change can be at the level of a block (coarse) or at the level of a row (fine-grained). The latter is provided by row-level dependency tracking. Refer to CREATE TABLE ... NOROWDEPENDENCIES | ROWDEPENDENCIES for more information on row-level dependency tracking. In the absence of row-level dependencies, ORA_ROWSCN reflects block-level dependencies.

Whether at the block level or at the row level, the ORA_ROWSCN should not be considered to be an exact SCN. For example, if a transaction changed row R in a block and committed at SCN 10, it is not always true that the ORA_ROWSCN for the row would return 10. While a value less than 10 would never be returned, any value greater than or equal to 10 could be returned. That is, the ORA_ROWSCN of a row is not always guaranteed to be the exact commit SCN of the transaction that last modified that row. However, with fine-grained ORA_ROWSCN, if two transactions T1 and T2 modified the same row R, one after another, and committed, a query on the ORA_ROWSCN of row R after the commit of T1 will return a value lower than the value returned after the commit of T2. If a block is queried twice, then it is possible for the value of ORA_ROWSCN to change between the queries even though rows have not been updated in the time between the queries. The only guarantee is that the value of ORA_ROWSCN in both queries is greater than the commit SCN of the transaction that last modified that row.

You cannot use the ORA_ROWSCN pseudocolumn in a query to a view. However, you can use it to refer to the underlying table when creating a view. You can also use this pseudocolumn in the WHERE clause of an UPDATE or DELETE statement.

ORA_ROWSCN is not supported for Flashback Query. Instead, use the version query pseudocolumns, which are provided explicitly for Flashback Query. Refer to the SELECT ... flashback_query_clause for information on Flashback Query and "Version Query Pseudocolumns" for additional information on those pseudocolumns.

Restriction on ORA_ROWSCN: This pseudocolumn is not supported for external tables.

Example The first statement below uses the ORA_ROWSCN pseudocolumn to get the system change number of the last operation on the employees table. The second statement uses the pseudocolumn with the SCN_TO_TIMESTAMP function to determine the timestamp of the operation:

SELECT ORA_ROWSCN, last_name
  FROM employees
  WHERE employee_id = 188;

SELECT SCN_TO_TIMESTAMP(ORA_ROWSCN), last_name
  FROM employees
  WHERE employee_id = 188;

See Also:

SCN_TO_TIMESTAMP