how can i modify or manipulate this trigger - mysql

Question

I'm trying to create a trigger which will capture any event that will occur when I update any column in the table before and after updating, let's say I have 4 columns:
first_name address city country
Let's say I edited first_name lets say Jack to Henk.
It should insert in another table the command (i.e. update) ,time , description but inside the description I want it to write Jack was changed to John by current user(i.e using the current-user () function),if it is a city being updated from Mechinkova to Tostov, it should do the same do with other columns.
I know I want to have to add the concat function inside the trigger, I want it to be like this for example:
DROP TRIGGER IF EXISTS adminpanel.soft//
CREATE TRIGGER adminpanel.soft BEFORE UPDATE ON adminpanel.aggrement
FOR EACH ROW
BEGIN
INSERT INTO adminpanel.aggretrigger(cmd, time, cmd_user, last_name, city) VALUES("INSERT", NOW(), CURRENT_USER(), new.last_name, new.city);
END
//

Answer 1

What you are asking for is an audit trigger. It is very easy to implement.
Let us first slightly modify your main table. Let's add a field id of integer datatype as the primary key to the table, so your table would look like:
tablename
( id integer PK
, first_name varchar
, address varchar
, city varchar
, country varchar
)
Now, you will need a table, say UNIVERSAL_AUDIT_ENTRY table that will store the changes made to the data in your schema.
From what experience I have, I suggest you create this table as follows:
universal_audit_entry
( universal_audit_entryid integer PK
, table_name varchar -- captures the name of the table
, column_name varchar -- captures the name of the column
, entry_type varchar -- captures the event, e.g., 'INSERT' or 'UPDATE'
, primary_key_value integer -- captures, e.g., the value in tblename.id
, from_str varchar -- captures the value that was present before
, to_str varchar -- captures the value that was changed into
, timestamp datetime -- captures the timestamp of the event
, username varchar -- captures the name of user
)
Now with the universal_audit_entry table ready, your trigger should look somewhat like:
CREATE TRIGGER adminpanel.soft
BEFORE UPDATE ON adminpanel.aggrement
FOR EACH ROW
BEGIN
IF UPDATING(first_name) THEN
INSERT INTO universal_audit_entry VALUES
( 123 -- example for universal_audit_entryid
, 'TABLENAME'
, 'FIRST_NAME'
, 'UPDATE'
, new.id
, old.first_name
, new.first_name
, current_timestamp()
, current_user);
END IF;
END;
//
You can use similar logic to audit more columns in the same table and other tables also.
Note:
This code is not tested. I have added it here only for illustration purposes. This code for trigger is not supposed to be used directly.
new and old are the pseudo-records that are generated during an update statement. These records correspond to the rows that are being updated. :new means the row after the update statement runs and :old means the row before the update statement runs. This works in Oracle. Kindly make sure if it works in MySQL also.
EDIT
You can read more about MySQL triggers here. Read more about audit trail here and this SO question.