How do I automatically update a timestamp in PostgreSQL

Question

I want the code to be able to automatically update the time stamp when a new row is inserted as I can do in MySQL using CURRENT_TIMESTAMP.

How will I be able to achi

Answer 1

To populate the column during insert, use a DEFAULT value:

CREATE TABLE users (
  id serial not null,
  firstname varchar(100),
  middlename varchar(100),
  lastname varchar(100),
  email varchar(200),
  timestamp timestamp default current_timestamp
)

Note that the value for that column can explicitly be overwritten by supplying a value in the INSERT statement. If you want to prevent that you do need a trigger.

You also need a trigger if you need to update that column whenever the row is updated (as mentioned by E.J. Brennan)

Note that using reserved words for column names is usually not a good idea. You should find a different name than timestamp

Answer 2

Using 'now()' as default value automatically generates time-stamp.

Answer 3

Updating timestamp, only if the values changed

Based on E.J's link and add a if statement from this link (https://stackoverflow.com/a/3084254/1526023)

CREATE OR REPLACE FUNCTION update_modified_column()
RETURNS TRIGGER AS $$
BEGIN
   IF row(NEW.*) IS DISTINCT FROM row(OLD.*) THEN
      NEW.modified = now(); 
      RETURN NEW;
   ELSE
      RETURN OLD;
   END IF;
END;
$$ language 'plpgsql';

Answer 4

You'll need to write an insert trigger, and possible an update trigger if you want it to change when the record is changed. This article explains it quite nicely:

http://www.revsys.com/blog/2006/aug/04/automatically-updating-a-timestamp-column-in-postgresql/

CREATE OR REPLACE FUNCTION update_modified_column()   
RETURNS TRIGGER AS $$
BEGIN
    NEW.modified = now();
    RETURN NEW;   
END;
$$ language 'plpgsql';

Apply the trigger like this:

CREATE TRIGGER update_customer_modtime BEFORE UPDATE ON customer FOR EACH ROW EXECUTE PROCEDURE  update_modified_column();