Postgres 17

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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), (100);

insert into B values (1), (200);

insert into C values (1), (2), (3), (300);

CREATE TABLE

CREATE TABLE

CREATE TABLE

INSERT 0 3

INSERT 0 2

INSERT 0 4

select * from
  (A left join B on a=b) left join C on a=c;

a
b
c

1
1
1

2
null
2

100
null
null

SELECT 3

select * from 
  A left join (B left join C on b=c) on a=b;

a
b
c

1
1
1

2
null
null

100
null
null

SELECT 3

a	b	c
1	1	1
2	null	2
100	null	null

a	b	c
1	1	1
2	null	null
100	null	null