Re: Virtual generated columns

drop table if exists gtest_err_1 cascade;
CREATE TABLE gtest_err_1 (
a int PRIMARY KEY generated by default as identity,
b int GENERATED ALWAYS AS (22),
d int default 22);
create view gtest_err_1_v as select * from gtest_err_1;
SELECT events & 4 != 0 AS can_upd, events & 8 != 0 AS can_ins,events &
16 != 0 AS can_del
FROM pg_catalog.pg_relation_is_updatable('gtest_err_1_v'::regclass,
false) t(events);

insert into gtest_err_1_v(a,b, d) values ( 11, default,33) returning *;
should the above query, b return 22?
even b is  "b int default" will return 22.


drop table if exists comment_test cascade;
CREATE TABLE comment_test (
  id int,
  positive_col int  GENERATED ALWAYS AS (22) CHECK (positive_col > 0),
  positive_col1 int  GENERATED ALWAYS AS (22) stored CHECK (positive_col > 0) ,
  indexed_col int,
  CONSTRAINT comment_test_pk PRIMARY KEY (id));
CREATE INDEX comment_test_index ON comment_test(indexed_col);
ALTER TABLE comment_test ALTER COLUMN positive_col1 SET DATA TYPE text;
ALTER TABLE comment_test ALTER COLUMN positive_col SET DATA TYPE text;
the last query should work just fine?


drop table if exists def_test cascade;
create table def_test (
    c0    int4 GENERATED ALWAYS AS (22) stored,
    c1    int4 GENERATED ALWAYS AS (22),
    c2    text default 'initial_default'
);
alter table def_test alter column c1 set default 10;
ERROR:  column "c1" of relation "def_test" is a generated column
HINT:  Use ALTER TABLE ... ALTER COLUMN ... SET EXPRESSION instead.
alter table def_test alter column c1 drop default;
ERROR:  column "c1" of relation "def_test" is a generated column

Is the first error message hint wrong?
also the second error message (column x is a generated column) is not helpful.
here, we should just say that cannot set/drop default for virtual
generated column?



drop table if exists bar1, bar2;
create table bar1(a integer, b integer GENERATED ALWAYS AS (22))
partition by range (a);
create table bar2(a integer);
alter table bar2 add column b integer GENERATED ALWAYS AS (22) stored;
alter table bar1 attach partition bar2 default;
this works, which will make partitioned table and partition have
different kinds of generated column,
but this is not what we expected?

another variant:
CREATE TABLE list_parted (
a int NOT NULL,
b char(2) COLLATE "C",
c int GENERATED ALWAYS AS (22)
) PARTITION BY LIST (a);
CREATE TABLE parent (LIKE list_parted);
ALTER TABLE parent drop column c, add column c int GENERATED ALWAYS AS
(22) stored;
ALTER TABLE list_parted ATTACH PARTITION parent FOR VALUES IN (1);




drop table if exists tp, tpp1, tpp2;
CREATE TABLE tp (a int NOT NULL,b text GENERATED ALWAYS AS (22),c
text) PARTITION BY LIST (a);
CREATE TABLE tpp1(a int NOT NULL, b text GENERATED ALWAYS AS (c
||'1000' ), c text);
ALTER TABLE tp ATTACH PARTITION tpp1 FOR VALUES IN (1);
insert into tp(a,b,c) values (1,default, 'hello') returning a,b,c;
insert into tpp1(a,b,c) values (1,default, 'hello') returning a,b,c;

select tableoid::regclass, * from tpp1;
select tableoid::regclass, * from tp;
the above two queries return different results, slightly unintuitive, i guess.
Do we need to mention it somewhere?



CREATE TABLE atnotnull1 ();
ALTER TABLE atnotnull1 ADD COLUMN c INT GENERATED ALWAYS AS (22), ADD
PRIMARY KEY (c);
ERROR:  not-null constraints are not supported on virtual generated columns
DETAIL:  Column "c" of relation "atnotnull1" is a virtual generated column.
I guess this error message is fine.

The last issue in the previous thread [1], ATPrepAlterColumnType
seems not addressed.

[1] https://postgr.es/m/CACJufxEGPYtFe79hbsMeOBOivfNnPRsw7Gjvk67m1x2MQggyiQ@mail.gmail.com