How to add 'created_at' and 'updated_at' columns?

 

According to the reference manual* you can use the DEFAULT CURRENT_TIMESTAMP and ON UPDATE CURRENT_TIMESTAMP clauses in column definitions:

With both DEFAULT CURRENT_TIMESTAMP and ON UPDATE CURRENT_TIMESTAMP, the column has the current timestamp for its default value and is automatically updated to the current timestamp.

whereas:

With a DEFAULT clause but no ON UPDATE CURRENT_TIMESTAMP clause, the column has the given default value and is not automatically updated to the current timestamp.

So, for example, you could use:

CREATE TABLE t1 (
  created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP ,
  updated_at DATETIME DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP
);

To add the columns to an already existing table you can use:

ALTER TABLE t1
ADD COLUMN created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
ADD COLUMN updated_at DATETIME DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP;

Source : Stackoverflow