Oracle TIMESTAMP_TO_SCN Function: A Simple Guide

The TIMESTAMP_TO_SCN function in Oracle SQL is a special function that does the exact opposite of SCN_TO_TIMESTAMP. It takes a TIMESTAMP value as an argument and returns the approximate System Change Number (SCN) associated with that time.

This function is a key component of Oracle's Flashback features, as it allows you to find the "database version" (the SCN) that corresponds to a specific point in time.

What is the TIMESTAMP_TO_SCN Function in Oracle?

The TIMESTAMP_TO_SCN(timestamp) function takes a TIMESTAMP and returns a NUMBER (the SCN).

This is useful for:

• Flashback Queries: Finding the SCN you need to use in a query like SELECT * FROM my_table AS OF SCN ....
• Auditing: Determining the SCN for a known event time, which you can then use to query other "AS OF" data.

Note: The association between a timestamp and an SCN is only stored for a limited time (e.g., a few days), which is controlled by your database's undo retention settings. You cannot use this function to find the SCN for a timestamp that is too old.

TIMESTAMP_TO_SCN Function Syntax

The syntax for TIMESTAMP_TO_SCN is very simple:

TIMESTAMP_TO_SCN(timestamp_value)

Let's break that down:

• timestamp_value: The TIMESTAMP you want to convert to an SCN.

Oracle TIMESTAMP_TO_SCN Function Examples

Here are two practical examples of how to use TIMESTAMP_TO_SCN.

Example 1: Finding the SCN of a Recent Event with TIMESTAMP_TO_SCN

This example shows how you could find the SCN of a row that was just inserted, assuming the row has a TIMESTAMP column.

Query:

-- First, let's assume a row was just inserted
-- INSERT INTO orders (order_id, order_date, ...)
-- VALUES (5000, SYSTIMESTAMP, ...);
-- COMMIT;

-- Now, let's query that row to find the SCN of its order_date
SELECT 
  TIMESTAMP_TO_SCN(order_date) AS "Order_SCN"
FROM 
  orders
WHERE 
  order_id = 5000;

Result: (The SCN will be a large number that varies on every system)

Order_SCN
------------
      574100

Example 2: Finding the SCN for a Specific Past Time with TIMESTAMP_TO_SCN

This example shows how to get the SCN for a specific point in the recent past, which you could then use for a Flashback Query.

Query:

-- What was the SCN 10 minutes ago?
SELECT 
  TIMESTAMP_TO_SCN(
    SYSTIMESTAMP - NUMTODSINTERVAL(10, 'MINUTE')
  ) AS "SCN_10_Minutes_Ago"
FROM DUAL;

Result: (This SCN could then be used in another query: SELECT * FROM employees AS OF SCN 574050)

SCN_10_Minutes_Ago
------------------
            574050