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
)
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 EJ Brennan )
Note that using reserved words for column names is usually not a good idea. You should find a different name than timestamp
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();
Updating timestamp, only if the values changed
Based on EJ'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';
使用 'now()' 作为默认值会自动生成时间戳。
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();
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();
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