Postgres 17

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-- https://kb.databasedesignbook.com/posts/sql-joins/

create table A (a integer not null primary key);

create table B (b integer not null primary key);

create table C (c integer not null primary key);

insert into A values (1), (2);

insert into B values (2);

insert into C values (2), (11), (12);

CREATE TABLE

CREATE TABLE

CREATE TABLE

INSERT 0 2

INSERT 0 1

INSERT 0 3

select * from
  (select * from A left join B on 1=1) AB left join C on 1 = 1;

a
b
c

1
2
2

1
2
11

1
2
12

2
2
2

2
2
11

2
2
12

SELECT 6

select *
  from A left join (select * from B left join C on 1=1) BC on 1 = 1;

a
b
c

1
2
2

1
2
11

1
2
12

2
2
2

2
2
11

2
2
12

SELECT 6

select * from
  (select * from A cross join B) AB cross join C;

a
b
c

1
2
2

1
2
11

1
2
12

2
2
2

2
2
11

2
2
12

SELECT 6

select *
  from A cross join (select * from B cross join C) BC;

a
b
c

1
2
2

1
2
11

1
2
12

2
2
2

2
2
11

2
2
12

SELECT 6