How to insert the selected data columns from one oracle database table into another oracle database table in real time

Question

I have a use case where I need to keep watch on table A in the oracle database XYZ by running a select statement with a where clause. If this select statement fetches any rows, then instantly I need to insert those rows into another table B which is another Oracle database MNO.

Also, suppose when I am in watch and the second time the same select statement retrieved a row which was already inserted in above step but now it has a change of values for few columns then, instantly the other table B should also get updated with this updated column value from table A.

Can I achieve this using shell scripting? Could anyone kindly let me know how to achieve this?

Many thanks for your suggestions in advance.

Answer 1

I'd say that merge is what you need:

merge into mno.table_2 b  -- or, possibly, table_2@mno
  using table_1 a
  on (a.id = b.id)
  when matched then update set
    (b.col1 = a.col1,
     b.col2 = a.col2
    )
  when not matched then insert (col1, col2)
    values (a.col1, a.col2);

Note line #1:

• if mno really is a "database" (and not just another user in the same database), then you'd have to use a database link (commented part of line #1)
• if mno is just another user, then it should grant select, insert, update on its table to user xyz ; otherwise, that operation won't work

Merge also means that you don't have to separately check whether that row exists in another table or not.

---

Shell scripting? Why? Keep everything within the database.

"Keep watch" can be done by

• creating a database trigger on xyz.table_1 so that as soon as something changes, it fires and runs merge
• or, schedule a job (using dbms_scheduler ) which will periodically (for example, every hour, twice a day, ...) run merge