Fetch changed data for table in Oracle Database to csv - sql

Question

I Need to fetch the changed data for table in oracle. Need help with the sql query which will fetch only the changed data for every 20 mins.
Or is there another workaround for this where we can fetch changed data?

Answer 1

If you know how to detect "only changed data" - I presume you must have some kind of a "timestamp" column - then that would be
select columns
from your_table
where timestamp_column >= sysdate - 20/(24*60);
because of this: 20 minutes / (24 hours in a day * 60 minutes in an hour)
SQL> alter session set nls_date_format = 'dd.mm.yyyy hh24:mi:ss'
Session altered.
SQL> select sysdate right_now,
2 sysdate - 20/(24*60) twenty_minutes_ago
3 from dual;
RIGHT_NOW TWENTY_MINUTES_AGO
------------------- -------------------
24.10.2019 08:40:18 24.10.2019 08:20:18
SQL>
How to create a CSV?
One option is to store your query into a .SQL file and use operating system's Task Scheduler (for MS Windows) or cron (for Unix) or whatever your operating system is. Let the script spool the result. There are numerous SQL*Plus SET options you can use to make the output pretty; for example:
set termout off
set trimspool on
set echo off
set verify off
set autoprint off
set serveroutput off
set arraysize 1000
set pagesize 0
set linesize 100
set long 10000
set numwidth 10
set feedback off
set colsep ';'
col empno format 99999
col ename format a10
col sal format 999G990
spool emps.txt
select empno, ename, sal from emp
where timestamp_column >= sysdate - 20/(24*60);
spool off
Another option is to create a stored procedure which will use UTL_FILE package and create that file in a directory (you'll have to talk to your DBA about it; it is - usually - on the database server; DBA should create a directory (as an Oracle object) and grant read/write privileges to you).
Then you'd create a database job (using DBMS_JOB or DBMS_SCHEDULER packages), scheduling it to run every 20 minutes.
Maybe the first one is simpler to implement; if nothing else, CSV is created on your local computer, not on the server.

Answer 2

You need a last_updated column of type datetime/date in your table. Then to get updated in last 20 minutes, the query can become like below.
select t.*
from table t
where t.last_updated >= sysdate - 20/(24*60)
where t is your tablename and last_updated is last updated datetime.

Answer 3

If you don't have a way to detect when rows change within the table then you can use a flashback query on your database (if it is set up to support it).
To get the new/modified rows:
SELECT *
FROM table_name
MINUS
SELECT *
FROM table_name AS OF TIMESTAMP( SYSTIMESTAMP - INTERVAL '20' MINUTE )
and to get the deleted rows:
SELECT *
FROM table_name AS OF TIMESTAMP( SYSTIMESTAMP - INTERVAL '20' MINUTE )
WHERE primary_key_column NOT IN ( SELECT primary_key_column FROM table_name )