MySQL 8.0

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create table `t1` (
  `date` date,
  `value` int
);

create table `t2` (
  `date` date,
  `value` int
);

insert into `t1` (`date`, `value`)
values ("2022-01-01", 1),
       ("2022-03-01", 3),
       ("2022-04-01", 4);
       
insert into `t2` (`date`, `value`)
values ("2022-01-01", 1),
       ("2022-02-01", 2),
       ("2022-04-01", 4);

Records: 3  Duplicates: 0  Warnings: 0



Records: 3  Duplicates: 0  Warnings: 0


select *
from `t1`
left join `t2` on `t2`.`date` = `t1`.`date`

union 

select *
from `t1`
right join `t2` on `t2`.`date` = `t1`.`date`;


date
value
date
value


2022-01-01
1
2022-01-01
1

2022-03-01
3
null
null

2022-04-01
4
2022-04-01
4

null
null
2022-02-01
2


select *
from `t1`
left join `t2` on `t2`.`date` = `t1`.`date`
where `t1`.`date` > "2022-01-01"

union

select *
from `t1`
right join `t2` on `t2`.`date` = `t1`.`date`
where `t1`.`date` > "2022-01-01";


date
value
date
value


2022-03-01
3
null
null

2022-04-01
4
2022-04-01
4


select *
from `t1`
left join `t2` on `t2`.`date` = `t1`.`date`
where `t1`.`date` > "2022-01-01"

union

select *
from `t1`
right join `t2` on `t2`.`date` = `t1`.`date`
where  `t2`.`date` > "2022-01-01";


date
value
date
value


2022-03-01
3
null
null

2022-04-01
4
2022-04-01
4

null
null
2022-02-01
2

date	value	date	value
2022-01-01	1	2022-01-01	1
2022-03-01	3	null	null
2022-04-01	4	2022-04-01	4
null	null	2022-02-01	2