Question

I am trying to write a before delete trigger on mysql table here’s is what I am trying to do exactly; I need a specific record to always be in the table so say for example the record is deleted or updated the trigger would simply reinsert the initial record.

EXAMPLE
Tablename: Users
Table Columns(3):ID,Username,Password
and I am trying to keep the following record from being deleted(Initial Record)
Username=Dames, Password=Password

However Im new to triggers and have been trying a thing or 3 but it really seems I need some help, I hope I made the question clear, and thanks alot.

Answer 1

1. If you’re happy to hard-code into the triggers the details of the record that you wish to preserve, then you could do something like:

   DELIMITER ;;
   
   CREATE TRIGGER foo_upd BEFORE UPDATE ON Users FOR EACH ROW
   IF OLD.Username <=> 'Dames' AND OLD.Password <=> 'Password' THEN
     INSERT INTO Users (Username, Password) VALUES ('Dames', 'Password');
   END IF ;;
   
   CREATE TRIGGER foo_del BEFORE DELETE ON Users FOR EACH ROW
   IF OLD.Username <=> 'Dames' AND OLD.Password <=> 'Password' THEN
     INSERT INTO Users (Username, Password) VALUES ('Dames', 'Password');
   END IF ;;
   
   DELIMITER ;
   

2. Otherwise, I’d recommend adding an additional boolean column to the Users table—e.g. locked:

   ALTER TABLE Users ADD COLUMN locked BOOLEAN NOT NULL DEFAULT FALSE;
   

   Then setting the value of that column to be TRUE on the record(s) that you wish to preserve:

   UPDATE Users SET locked = TRUE
   WHERE  Username = 'Dames' AND Password = 'Password';
   

   Then creating triggers along the following lines:

   DELIMITER ;;
   
   CREATE TRIGGER foo_upd BEFORE UPDATE ON Users FOR EACH ROW
   IF OLD.locked THEN
     INSERT INTO Users (Username, Password) VALUES (OLD.Username, OLD.Password);
   END IF ;;
   
   CREATE TRIGGER foo_del BEFORE DELETE ON Users FOR EACH ROW
   IF OLD.locked THEN
     INSERT INTO Users (Username, Password) VALUES (OLD.Username, OLD.Password);
   END IF ;;
   
   DELIMITER ;