If you need to determine if the value is changing, you'll still need to code comparison logic for :old and :new values.Like a stored procedure, a trigger is a named PL/SQL unit that is stored in the database and can be invoked repeatedly. UPDATE bank_transactions SET txn_number = 'NEWTXN8080' WHERE txn_id = 1; UPDATE bank_transactions SET txn_number = 'NEWTXN9595' WHERE txn_id = 2; -- output 1 rows updated. Dhaval Dadhaniya is a software engineer by profession and reader/writter by passion. CREATED_DATE); END; --Inserting values INSERT INTO BANK_TRANSACTIONS values ('1','TXN1234','Peter Thomas','12-MAY-2017','HR',sysdate); INSERT INTO BANK_TRANSACTIONS values ('2','TXN9999','Jemes Patel','10-JUN-2016','HR',sysdate); select * from BANK_TRANSACTIONS; --updating values.LAST_APPLIED_DATE,'DD-MON-YYYY'))/12 INTO years_since_last_applied FROM dual; -- Check whether years_since_last_applied is greater than 2 years or not IF (years_since_last_applied -- setting date format to to 'DD-MON-YYYY' alter session set nls_date_format = 'DD-MON-YYYY'; INSERT INTO job_openings VALUES (1,'Mark','Sharma',10,'01-JAN-2012'); INSERT INTO job_openings VALUES (2,'Praveen','Kumar',4,'01-DEC-2010'); INSERT INTO job_openings VALUES (3,'Rahul','Kohli',6,null); -- output 1 rows inserted. TRG_BEFORE_EMP_UPDATE' -- Try to update last_Applied_Date which is less than 2 years UPDATE job_openings SET LAST_APPLIED_DATE = '10-JUN-2016' where APPLICATION_ID = 3; -- error Error report - ORA-20000: Previous application attempt must not be done in last 2 years. TRG_BEFORE_EMP_UPDATE", line 15 ORA-04088: error during execution of trigger 'SYSTEM. UPDATED_DATE := sysdate; END; -- setting date format to to 'DD-MON-YYYY' alter session set nls_date_format = 'DD-MON-YYYY'; INSERT INTO person_records VALUES (101,'Devil','Khedut',sysdate,null,null); INSERT INTO person_records VALUES (102,'Kanji','Yadav',sysdate,null,null); -- output 1 rows inserted. CREATE TABLE bank_transactions_audit ( TXN_ID number(10), TXN_NUMBER varchar2(20), PARTY_NAME varchar2(50), TXN_DATE date, CREATED_BY varchar2(20), CREATED_DATE date ); --Creating Trigger CREATE OR REPLACE TRIGGER trg_before_update_txn_audit BEFORE UPDATE ON bank_transactions FOR EACH ROW BEGIN -- Insert OLD values in audit table for logging purpose INSERT INTO bank_transactions_audit VALUES(: OLD. TRG_BEFORE_EMP_UPDATE' --Creating person_records table. CREATE TABLE person_records ( PERSON_ID number(10) primary key, FIRST_NAME varchar2(50), LAST_NAME varchar2(50), HIRE_DATE date, UPDATED_BY varchar2(20), UPDATED_DATE date ); CREATE OR REPLACE TRIGGER trg_before_person_update BEFORE UPDATE on person_records FOR EACH ROW DECLARE username varchar2(20); BEGIN SELECT USER INTO username FROM dual; -- Setting updated_by and updated_Date values. Specifically: How Triggers and Constraints Differ Both triggers and constraints can constrain data input, but they differ significantly. For example, a trigger can prevent a DML statement from inserting a values that were inserted into the column before the trigger was defined or while the trigger was disabled.
SQL statements running in triggers follow the same rules that standalone SQL statements do.Many applications update all of the columns in a table -- setting them to their old value, rather then trying to figure out exactly which columns have been updated by the client. create or replace trigger test_trigger 2 after update of x,y on test 3 for each row 4 begin 5 if updating( 'X' ) then 6 dbms_output.put_line( 'X is being updated' ); 7 end if; 8 9 if updating( 'Y' ) then 10 dbms_output.put_line( 'Y is being updated' ); 11 end if; 12 end; 13 / Trigger created.SQL Notice in the last update it indicated that x and y both were being updated (which they were), but the update didn't change the value (both x and y were 1 prior to the update which set them to 1). You can use updating (column) but it will only tell you that the column itself is being updated and not if the value has changed.However, triggers can enforce some complex business rules that constraints cannot.Oracle strongly recommends that you use triggers to constrain data input only in these situations: created on a table or editioning view can fire at one, some, or all of the preceding timing points.Constraint behavior depends on constraint state, as explained in .Constraints are easier to write and less error-prone than triggers that enforce the same rules.Vishwanath Dalvi is a gifted engineer and tech enthusiast. When not hacking around or supporting the open source community, he is trying to overcome his phobia of dogs. It works, but it won't tell you if the value changed, only that the column is being updated (even if the update doesn't change the value).CREATE or REPLACE TRIGGER emp_after_insert AFTER INSERT ON emp FOR EACH ROW DECLARE BEGIN insert into emp_backup values (:new.empid, :new.fname, :new.lname); DBMS_OUTPUT.PUT_LINE('Record successfully inserted into emp_backup table'); END; Second Problem: We want o update a record in the ’emp_backup’ table if a corresponding record is updated in the ’emp’ table.