SQL trigger for tracking history of changes - ORACLE DB - sql

Question

I have a table cust_info and need to track the update and delete on it. I created 2 new tables ( archive_customers is the same as cust_info but customers_hist contains two additional instances (changed_by and change_date)).
CREATE TABLE CUST_INFO
(
CUST_ID NUMBER(15),
CUST_F_NAME VARCHAR(20),
CUST_L_NAME VARCHAR(20),
CUST_ADDRESS VARCHAR(40),
CITY VARCHAR(30),
STATE VARCHAR(30),
ZIP NUMBER,
PHONE VARCHAR(12),
PRIMARY KEY (CUST_ID)
);
I was searching for similar problems and this is what I got so far:
CREATE OR REPLACE TRIGGER TRIGGER_UPDATE
BEFORE UPDATE ON CUST_INFO
FOR EACH ROW
BEGIN
INSERT INTO CUSTOMERS_HIST
(
CUST_ID,
CUST_F_NAME,
CUST_L_NAME,
CUST_ADDRESS,
CITY,
STATE,
ZIP,
PHONE,
SYSDATE
)
SELECT
OLD.CUST_ID,
OLD.CUST_F_NAME,
OLD.CUST_L_NAME,
OLD.CUST_ADDRESS,
OLD.CITY,
OLD.STATE,
OLD.ZIP,
OLD.PHONE
FROM CUST_INFO
END;
CREATE OR REPLACE TRIGGER TRIGGER_DELETE
BEFORE DELETE ON CUST_INFO
FOR EACH ROW
BEGIN
INSERT INTO ARCHIVE_CUSTOMERS
(
CUST_ID,
CUST_F_NAME,
CUST_L_NAME,
CUST_ADDRESS,
CITY,
STATE,
ZIP,
PHONE
)
SELECT
OLD.CUST_ID,
OLD.CUST_F_NAME,
OLD.CUST_L_NAME,
OLD.CUST_ADDRESS,
OLD.CITY,
OLD.STATE,
OLD.ZIP,
OLD.PHONE
FROM CUST_INFO
END;
In addition, I am not sure how to get the change_by and change_date populated??
If you need more info, please make a comment.
Thank you

Answer 1

Perhaps you could use the user and sysdate built-in functions for chnage_by and change_date respectively. The code I would write is completely different if I want to store the change history in a table. Yet, for your example, the code is as follows:
CREATE OR REPLACE TRIGGER TRIGGER_UPDATE
BEFORE UPDATE
ON CUST_INFO
FOR EACH ROW
BEGIN
INSERT INTO CUSTOMERS_HIST (CUST_ID,
CUST_F_NAME,
CUST_L_NAME,
CUST_ADDRESS,
CITY,
STATE,
ZIP,
PHONE,
SYSDATE,
change_by,
change_date)
SELECT OLD.CUST_ID,
OLD.CUST_F_NAME,
OLD.CUST_L_NAME,
OLD.CUST_ADDRESS,
OLD.CITY,
OLD.STATE,
OLD.ZIP,
OLD.PHONE,
user,
sysdate
FROM CUST_INFO;
END;
/
CREATE OR REPLACE TRIGGER TRIGGER_DELETE
BEFORE DELETE
ON CUST_INFO
FOR EACH ROW
BEGIN
INSERT INTO ARCHIVE_CUSTOMERS (CUST_ID,
CUST_F_NAME,
CUST_L_NAME,
CUST_ADDRESS,
CITY,
STATE,
ZIP,
PHONE,
change_by,
change_date)
SELECT OLD.CUST_ID,
OLD.CUST_F_NAME,
OLD.CUST_L_NAME,
OLD.CUST_ADDRESS,
OLD.CITY,
OLD.STATE,
OLD.ZIP,
OLD.PHONE,
user,
sysdate
FROM CUST_INFO;
END;
/
That was the answer for your question.
Now, if I were you, I would build an audit table as follows:
TABLE audit_entry
(
audit_Entry_Id INTEGER,
change_By VARCHAR2 (30), -- User who made the change
change_TS TIMESTAMP, -- TS at which the change was made
table_Name VARCHAR2 (30), -- Name of table on which change was made
column_Name VARCHAR2 (30), -- Name of column in that table
primary_key_id INTEGER, -- The PK or ID of the row which was changed
old_clob CLOB,
new_clob CLOB,
old_TS TIMESTAMP,
new_TS TIMESTAMP,
old_number NUMBER (36, 2),
new_number NUMBER (36, 2)
)
The last old and new columns would store the old and new values of appropriate data type. You could also improve the table as per your needs. Then, build a trigger on your tables to track changes and insert values into audit_entry table accordingly.