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Lets create a compound trigger for auditing a large table called ’employees’. Similarly any such pre-processing if required can be performed on that source table (mutating table), doing so will avoid any possible mutating-error.Any changes made in any field of ’employees’ table needs to be logged in as a separate row in audit table ‘aud_empl’. For e.g., consider the same example with another restriction, “Any update of salary should be such that it is not less than 1/12th of maximum salary of any employee, or else an error is raised”.Luckily enough, we can fake a staging table using DUAL: create table employees ( employee_id integer not null, employee_name varchar2(100) not null); alter table employees add constraint employee_pk primary key (employee_id); create or replace procedure merge_employee( i_emp_id in integer, i_emp_name in varchar2 ) is begin merge into employees e using (select i_emp_id id, i_emp_name name from dual) s on (e.employee_id = s.id) when matched then update set employee_name = when not matched then insert (employee_id, employee_name) values (s.id, s.name); end; / With the merge statement, we now have a single more complex query instead of the 3 we started with, or the two of the refined approach.
If you need to determine if the value is changing, you'll still need to code comparison logic for :old and :new values.Plus there is an added advantage: it allows sharing of common state between all the trigger-points using variable.This is because compound trigger in oracle 11g has a declarative section where one can declare variable to be used within trigger.create table Employee( 2 ID VARCHAR2(4 BYTE) NOT NULL, 3 First_Name VARCHAR2(10 BYTE), 4 Last_Name VARCHAR2(10 BYTE), 5 Start_Date DATE, 6 End_Date DATE, 7 Salary Number(8,2), 8 City VARCHAR2(10 BYTE), 9 Description VARCHAR2(15 BYTE) 10 ) 11 / Table created.SQL select * from Employee 2 / ID FIRST_NAME LAST_NAME START_DAT END_DATE SALARY CITY DESCRIPTION ---- -------------------- -------------------- --------- --------- ---------- ---------- --------------- 01 Jason Martin 25-JUL-96 25-JUL-06 1234.56 Toronto Programmer 02 Alison Mathews 21-MAR-76 21-FEB-86 6661.78 Vancouver Tester 03 James Smith 12-DEC-78 15-MAR-90 6544.78 Vancouver Tester 04 Celia Rice 24-OCT-82 21-APR-99 2344.78 Vancouver Manager 05 Robert Black 15-JAN-84 08-AUG-98 2334.78 Vancouver Tester 06 Linda Green 30-JUL-87 04-JAN-96 4322.78 New York Tester 07 David Larry 31-DEC-90 12-FEB-98 7897.78 New York Manager 08 James Cat 17-SEP-96 15-APR-02 1232.78 Vancouver Tester 8 rows selected.
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You can also perform more complicated updates in Oracle.