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Updating external tables in Oracle

September 1, 2005

Oracle external tables are great for incorporating external metadata for an Oracle data warehouse and the table data resides on the server as a flat file while supporting Oracle SQL.

You can also use external tables as "csv" files, allowing the external table data to be used inside a Microsoft Excel spreadsheets.

Peter Kok has published a very cleaver technique to make Oracle external tables accept updates.  He lists he steps:

The trick we will use to make DML possible consists of three steps:

  1. Define a view on the external table.
     
  2. On this view, define INSTEAD OF triggers for insert, update and delete.
     
  3. Write PL/SQL code in these triggers to perform the required processing.

Kok then shows examples of the code and offers a free download of his technique, and offers important caveats:

The problem is with doing a multiple delete (i.e. a delete statement that affects more than one row). As we noted before, the INSTEAD OF trigger is implicitly for each row. This means statement-level information is unavailable.

create or replace view emp_ext_tab_vw
as
  select       rownum         rownumber
         , emp.empno          empno
         , emp.ename          ename
         , emp.job            job
         , emp.mgr            mgr
         , emp.hiredate       hiredate
         , emp.sal            sal
         , emp.comm           comm
         , emp.deptno         deptno
  from     emp_ext_tab        emp
  order by rownumber asc
/
 

create or replace trigger emp_ext_tab_vw_brd
instead of delete on emp_ext_tab_vw
begin
  --
  emp_ext_tab_dml.delete_record ( :OLD.rownumber );
  --
end;
/

 

 
 
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