How do I automatically update a timestamp in PostgreSQL - database

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 achieve this in PostgreSQL?
CREATE TABLE users (
id serial not null,
firstname varchar(100),
middlename varchar(100),
lastname varchar(100),
email varchar(200),
timestamp timestamp
)

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

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();

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

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

Answer 5

To automatically update the timestamp field in PostgresSQL whenever a new row is inserted, you can set the current_timestamp as its 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
)
In addition to this, you might want to prevent anyone from updating this field in the future, and this can be done by creating an update trigger and applying it:
CREATE OR REPLACE FUNCTION stop_change_on_timestamp()
RETURNS trigger AS
$BODY$
BEGIN
-- always reset the timestamp to the old value ("actual creation time")
NEW.timestamp := OLD.timestamp;
RETURN NEW;
END;
$BODY$
CREATE TRIGGER prevent_timestamp_changes
BEFORE UPDATE
ON users
FOR EACH ROW
EXECUTE PROCEDURE stop_change_on_timestamp();

Answer 6

For update and Liquibase YAML:
databaseChangeLog:
- changeSet:
id: CREATE FUNCTION set_now_to_timestamp
author: Konstantin Chvilyov
changes:
- sql:
sql: CREATE OR REPLACE FUNCTION set_now_to_timestamp() RETURNS TRIGGER LANGUAGE plpgsql AS 'BEGIN NEW.timestamp = NOW(); RETURN NEW; END;'
- changeSet:
id: CREATE TRIGGER update_users_set_now_to_timestamp
author: Konstantin Chvilyov
changes:
- sql:
sql: CREATE TRIGGER update_users_set_now_to_timestamp BEFORE UPDATE ON users FOR EACH ROW EXECUTE PROCEDURE set_now_to_timestamp();