Postgres 16

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

create table table1(col1, col2, col3, col4) as values
 (1,	'a',	'x1',	'asdc')
,(2,	'b',	'x2',	'czxa')
,(3,	'c',	'x3',	'xfsdaa');

create table table2(col2,col3) as values
 ('l',	'x56')
,('q',	'x99')
,('c',	'x3');

select col1, col2, col3, col4 from table1
union all
select null,col2,col3,null from table2;

SELECT 3



SELECT 3




col1
col2
col3
col4


1
a
x1
asdc

2
b
x2
czxa

3
c
x3
xfsdaa

null
l
x56
null

null
q
x99
null

null
c
x3
null



SELECT 6


select * from table1 natural full outer join table2;


col2
col3
col1
col4


a
x1
1
asdc

b
x2
2
czxa

c
x3
3
xfsdaa

l
x56
null
null

q
x99
null
null



SELECT 5


select * 
from (select tableoid::regclass,null as force_mismatch,* from table1) a
natural full outer join
     (select tableoid::regclass,null as force_mismatch,* from table2) b;


tableoid
force_mismatch
col2
col3
col1
col4


table1
null
a
x1
1
asdc

table1
null
b
x2
2
czxa

table1
null
c
x3
3
xfsdaa

table2
null
c
x3
null
null

table2
null
l
x56
null
null

table2
null
q
x99
null
null



SELECT 6

col1	col2	col3	col4
1	a	x1	asdc
2	b	x2	czxa
3	c	x3	xfsdaa
null	l	x56	null
null	q	x99	null
null	c	x3	null

tableoid	force_mismatch	col2	col3	col1	col4
table1	null	a	x1	1	asdc
table1	null	b	x2	2	czxa
table1	null	c	x3	3	xfsdaa
table2	null	c	x3	null	null
table2	null	l	x56	null	null
table2	null	q	x99	null	null