Get oldest timestamp from each user_id - mysql

Question

Database of "sales"
Each "sold_by" is the person who essentially has made that particular sale. My aim is to get the most recent "sale_date" grouped by "sold_by" to return one record for each unique "sold_by" record (which is stored as an integer in my database, but this is an example)
╔═════════╦═════════╦══════════════════╗
║ sale_id ║ sold_by ║ sale_date ║
╠═════════╬═════════╬══════════════════╣
║ 0 ║ PETER ║ 01/01/2017 00:00 ║
║ 1 ║ JOHN ║ 01/01/2017 00:00 ║
║ 2 ║ PETER ║ 30/03/2017 00:00 ║
║ 3 ║ JOHN ║ 03/02/2017 00:00 ║
║ 4 ║ SIMON ║ 04/02/2017 00:00 ║
║ 5 ║ JOHN ║ 05/01/2017 00:00 ║
║ 6 ║ SIMON ║ 26/01/2017 00:00 ║
║ 7 ║ PETER ║ 07/01/2017 00:00 ║
║ 8 ║ SIMON ║ 28/01/2017 00:00 ║
║ 9 ║ JOHN ║ 09/01/2017 00:00 ║
║ 0 ║ PETER ║ 20/01/2017 00:00 ║
╚═════════╩═════════╩══════════════════╝
Database example for account_manager_sellers (please note, the ID matches sold_by in the table above.
╔════╦══════════════╗
║ id ║ company_name ║
╠════╬══════════════╣
║ 0 ║ PETER ║
║ 1 ║ JOHN ║
║ 2 ║ SIMON ║
╚════╩══════════════╝
The example below works but is not working as desired, it is not getting MIN or MAX date but seemingly returning a random date from the middle of the database.
SELECT `sold_by`, `sale_date`
FROM `sales`
NATURAL JOIN (
SELECT `sold_by`, MAX(`sale_date`) AS entry_date
FROM `sales`
GROUP BY `sold_by`
) AS tmin
JOIN `account_manager_sellers` USING (`id`)
WHERE `sale_date` < '2017-03-31 00:00:00';
So ultimately, I need to get ONE record for each unique sold_by but it needs to be the most recent date. So from the first table above it would return:
+---+-------+------------------+
| 2 | PETER | 30/03/2017 00:00 |
+---+-------+------------------+
| 3 | JOHN | 03/02/2017 00:00 |
+---+-------+------------------+
| 4 | SIMON | 04/02/2017 00:00 |
+---+-------+------------------+
P.S I also tried removing the MAX(sale_date) from the sub query, and replacing that with an ORDER BY sale_date LIMIT 1 (but obviously it only returned one sole result)

Answer 1

The basic query you want might look something like this:
SELECT p1.*
FROM plans p1
INNER JOIN
(
SELECT seller_id, MAX(plan_written) AS entry_date
FROM plans
GROUP BY seller_id
) p2
ON p1.seller_id = p2.seller_id AND
p1.plan_written = p2.entry_date;
You also have another join to the account_manager_sellers table, but since I can't see your table definitions, don't know your columns, etc., I won't attempt an answer for that.
You might want to move away from using natural joins, because they can obfuscate the join conditions in your query.