MYSQL Max Value of status - mysql

Question

I have the following tables that records the details of letters vs actions, taken for them.
letter table
+-----------+-------------+
| letter_id | description |
+-----------+-------------+
| 1 | A |
| 2 | B |
| 3 | C |
| 4 | D |
+-----------+-------------+
action table
+-----------+--------+------------+---------------+
| action_id | ref_no | date | action_status |
+-----------+--------+------------+---------------+
| 1 | 1 | 2018-09-20 | On-Going |
| 2 | 1 | 2018-09-22 | Finished |
| 3 | 3 | 2018-09-16 | On-Going |
| 4 | 4 | 2018-09-26 | On-Going |
| 5 | 4 | 2018-09-27 | Finished |
+-----------+--------+------------+---------------+
And need to get the following output
+-----------+-------------+------------+---------------+
| letter_id | description | date | action_status |
+-----------+-------------+------------+---------------+
| 1 | A | 2018-09-22 | Finished |
| 2 | B | - | Pending |
| 3 | C | 2018-09-16 | On-Going |
| 4 | D | 2018-09-27 | Finished |
+-----------+-------------+------------+---------------+
I used the following query
select letter.letter_id,letter.description, action.date, action.action_status
from letter
left join action on letter.letter_id=action.ref_no
where (date in
(
select max(date) from action
where letter.letter_id=action.ref_no
))
But the above query generate the following output
+-----------+-------------+------------+---------------+
| letter_id | description | date | action_status |
+-----------+-------------+------------+---------------+
| 1 | A | 2018-09-20 | On-Going |
| 1 | A | 2018-09-22 | Finished |
| 2 | B | - | Pending |
| 3 | C | 2018-09-16 | On-Going |
| 4 | D | 2018-09-26 | On-Going |
| 4 | D | 2018-09-27 | Finished |
+-----------+-------------+------------+---------------+
I can not understand what I am going wrong. Can anyone help me ?

Answer 1

DROP TABLE IF EXISTS action;
CREATE TABLE action
(action_id SERIAL PRIMARY KEY
,letter_id INT NOT NULL
,date DATE NOT NULL
,action_status VARCHAR(20) NOT NULL
);
INSERT INTO action VALUES
(1,101,'2018-09-20','On-Going'),
(2,101,'2018-09-22','Finished'),
(3,103,'2018-09-16','On-Going'),
(4,104,'2018-09-26','On-Going'),
(5,104,'2018-09-27','Finished');
SELECT x.*
FROM action x
JOIN
( SELECT letter_id, MAX(date) max_date FROM action GROUP BY letter_id ) y
ON y.letter_id = x.letter_id
AND y.max_date = x.date;
+-----------+-----------+------------+---------------+
| action_id | letter_id | date | action_status |
+-----------+-----------+------------+---------------+
| 2 | 101 | 2018-09-22 | Finished |
| 3 | 103 | 2018-09-16 | On-Going |
| 5 | 104 | 2018-09-27 | Finished |
+-----------+-----------+------------+---------------+
Presumably, you can figure out the rest