MySQL 8.0

By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.

CREATE TABLE a SELECT 'a' x UNION SELECT 'b';
CREATE TABLE b SELECT 'a' x UNION SELECT 'c';
CREATE TABLE c SELECT 'b' x UNION SELECT 'c';

Records: 2  Duplicates: 0  Warnings: 0

Records: 2  Duplicates: 0  Warnings: 0

Records: 2  Duplicates: 0  Warnings: 0

select a.*, b.*, c.*
from a left join b using (x) left join c using (x)

x
x
x

a
a
null

b
null
b

select a.*, b.*, c.*
from a left join (b left join c using (x))  using (x)

x
x
x

a
a
null

b
null
null

x	x	x
a	a	null
b	null	b

x	x	x
a	a	null
b	null	null