Problem

Given a table of employee data, write a SQL trigger that will automatically update the "last_updated" column whenever a change is made to any of the other columns in the table.
Example input:
Employee table with columns: id, first_name, last_name, start_date, end_date, last_updated
id | first_name | last_name | start_date | end_date | last_updated
1 | John | Doe | 01/01/2018 | NULL | 01/01/2018
2 | Jane | Smith | 02/01/2018 | NULL | 02/01/2018
3 | Bill | Gates | 03/01/2018 | NULL | 03/01/2018
Example output:
Employee table with columns: id, first_name, last_name, start_date, end_date, last_updated
id | first_name | last_name | start_date | end_date | last_updated
1 | John | Doe | 01/01/2018 | NULL | 01/02/2018
2 | Jane | Smith | 02/01/2018 | NULL | 02/02 /2018
3 | Bill | Gates | 03/01/2018 | NULL | 03/02/2018

Solution

CREATE TRIGGER update_last_updated
AFTER UPDATE ON employee
FOR EACH ROW
BEGIN
  UPDATE employee
  SET last_updated = CURRENT_TIMESTAMP
  WHERE id = NEW.id;
END;

/*

The trigger above is optimal because it will update the last_updated column for every row that is updated.

*/