Question

I want to create a trigger in Oracle 11g. The problem is that I want a trigger which runs every time when there is a SELECT statement. Is this possible or is there other way to achieve the same result. This is the PL/SQL block:

CREATE TRIGGER time_check
   BEFORE INSERT OR UPDATE OF users, passwd, last_login ON table
   FOR EACH ROW
   BEGIN
      delete from table where last_login < sysdate - 30/1440;
   END;

I’m trying to implement a table where I can store user data. I want to “flush” the rows which are old than one hour. Are there other alternatives to how I could implement this?

p.s Can you tell me is this PL/SQL block is correct. Are there any mistakes?

BEGIN
sys.dbms_scheduler.create_job(
job_name => '"ADMIN"."USERSESSIONFLUSH"',
job_type => 'PLSQL_BLOCK',
job_action => 'begin
   -- Insert PL/SQL code here
   delete from UserSessions where last_login < sysdate - 30/1440;
end;',
repeat_interval => 'FREQ=MINUTELY;INTERVAL=2',
start_date => systimestamp at time zone 'Asia/Nicosia',
job_class => '"DEFAULT_JOB_CLASS"',
comments => 'Flushes expired user sessions',
auto_drop => FALSE,
enabled => FALSE);
sys.dbms_scheduler.set_attribute( name => '"ADMIN"."USERSESSIONFLUSH"', attribute => 'job_priority', value => 5);
sys.dbms_scheduler.set_attribute( name => '"ADMIN"."USERSESSIONFLUSH"', attribute => 'logging_level', value => DBMS_SCHEDULER.LOGGING_FAILED_RUNS);
sys.dbms_scheduler.enable( '"ADMIN"."USERSESSIONFLUSH"' );
END;

Answer 1

I’m not aware of a way of having a trigger on select. From the documentation, the only statements you can trigger on are insert/delete/update (and some DDL).

For what you want to do, I would suggest a simpler solution: use the DBMS_SCHEDULER package to schedule a cleanup job every so often. It won’t add overhead to your select queries, so it should have less performance impact globally.

You’ll find lots of examples in: Examples of Using the Scheduler