Postgres 14

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select version();

version

PostgreSQL 14.10 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 8.5.0 20210514 (Red Hat 8.5.0-20), 64-bit

SELECT 1

create table test( ts timestamp without time zone );

CREATE TABLE

insert into test(ts) values (now());
select * from test;

INSERT 0 1

ts

2024-07-10 22:05:21.948968

SELECT 1

alter table test add gts date generated always as ( ts::date) stored;               
select * from test;

ALTER TABLE

ts
gts

2024-07-10 22:05:21.948968
2024-07-10

SELECT 1

insert into test(ts) values (now());
select * from test;

INSERT 0 1

ts
gts

2024-07-10 22:05:21.948968
2024-07-10

2024-07-10 22:05:21.961668
2024-07-10

SELECT 2

ts	gts
2024-07-10 22:05:21.948968	2024-07-10
2024-07-10 22:05:21.961668	2024-07-10