trigger to create new row every 30 days How can I create trigger for table to insert a row every 30 day?

ID  Date        Days
1   10/7/2016    0
2   09/8/2016    30  
3   08/9/2016    60
A trigger is executed as result of a certain event (e.g insert/update/delete on a table). You need something like a job scheduler. 

You did not specified the database. By example Oracle has something like:

DBMS_SCHEDULER.CREATE_JOB(....