Computed / calculated / virtual / derived columns in PostgreSQL

Question

Does PostgreSQL support computed / calculated columns, like MS SQL Server? I can\'t find anything in the docs, but as this feature is included in many other DBMSs I thought

Answer 1

One way to do this is with a trigger!

CREATE TABLE computed(
    one SERIAL,
    two INT NOT NULL
);

CREATE OR REPLACE FUNCTION computed_two_trg()
RETURNS trigger
LANGUAGE plpgsql
SECURITY DEFINER
AS $BODY$
BEGIN
    NEW.two = NEW.one * 2;

    RETURN NEW;
END
$BODY$;

CREATE TRIGGER computed_500
BEFORE INSERT OR UPDATE
ON computed
FOR EACH ROW
EXECUTE PROCEDURE computed_two_trg();

The trigger is fired before the row is updated or inserted. It changes the field that we want to compute of NEW record and then it returns that record.