Postgres 13

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CREATE TABLE person(
   id BIGINT,
   name VARCHAR(50),
   last_name VARCHAR(50)
)

CREATE TABLE

alter table person add column full_name text generated always as
    (name || last_name) stored;

ALTER TABLE

insert into person (id, name, last_name) values (1, 'a', 'b')

INSERT 0 1

select * from person

id
name
last_name
full_name

1
a
b
ab

SELECT 1