Join to another table only matching specific records - mysql

Question

I have a table of ports:
drop table if exists ports;
create table ports(id int, name char(20));
insert into ports (id, name ) values
(1, 'Port hedland'),
(2, 'Kwinana');
And a table of tariffs connected to those ports:
drop table if exists tariffs;
create table tariffs(id int, portId int, price decimal(12,2), expiry bigint(11));
insert into tariffs (id, portId, price, expiry ) values
(1, 2, 11.00, 1648408400),
(2, 2, 12.00, 1648508400),
(3, 2, 13.00, 1648594800),
(4, 2, 14.00, 1651273200),
(5, 2, 15.00, 2250000000 );
insert into tariffs (id, portId, price, expiry ) values
(1, 1, 21.00, 1648408400),
(2, 1, 22.00, 1648508400),
(3, 1, 23.00, 1648594800),
(4, 1, 24.00, 1651273200),
(5, 1, 25.00, 2250000000 );
Each tariff has an expiry.
I can easily make a query to figure out the right tariff for as specific date for each port. For example at timestamp 1648594700 the right tariff is:
SELECT * FROM tariffs
WHERE 1648594700 < expiry AND portId = 2
ORDER BY expiry
LIMIT 1
Result:
id portId price expiry
3 2 13.00 1648594800
However, in my application I want to be able to pull in the right tariff starting from the ports record.
For one record, I can do this:
SELECT * FROM ports
LEFT JOIN tariffs on tariffs.portId = ports.id
WHERE 1648594700 < tariffs.expiry AND ports.id = 2
LIMIT 1
Result:
id name id portId price expiry
2 Kwinana 3 2 13.00 1648594800
This feels a little 'dirty', especially because I am doing a lookup on a record, and then forcing only one result using LIMIT. But, OK.
What I cannot do, and can't work out how to do, is a query that will return a list of ports, and each port having a price field that matches the constraint above (that is, the record with the highest expiry compared to 1648594700 for each port).
This obviously won't work:
SELECT * FROM ports
left join tariffs on tariffs.portId = ports.id
where 1648594700 < tariffs.expiry
Since the result of the query, testing with timestamp 1648594700, would be:
id name id portId price expiry
2 Kwinana 3 2 13.00 1648594800
2 Kwinana 4 2 14.00 1651273200
2 Kwinana 5 2 15.00 2250000000
1 Port he 3 1 23.00 1648594800
1 Port he 4 1 24.00 1651273200
1 Port he 5 1 25.00 2250000000
Instead, the result for all ports (before further filtering) should be:
id name id portId price expiry
2 Kwinana 3 2 13.00 1648594800
1 Port he 3 1 23.00 1648594800
Is there a clean, non-hacky way to have such a result?
As an added constraint, is this possible for this to be done in ONE query, without temp tables etc.?

Answer 1

You can select the lowest expiry, do your join and only take the rows having this minimum expiry:
SELECT p.id, p.name, t.id, t.portId, t.price, t.expiry
FROM ports p
LEFT JOIN tariffs t ON p.id = t.portId
WHERE expiry = (SELECT MIN(expiry) FROM tariffs WHERE 1648594700 < expiry)
ORDER BY p.id;
This will get your desired result, please see here: db<>fiddle

Answer 2

On MySQL 8+, ROW_NUMBER should work here:
WITH cte AS (
SELECT p.id, p.name, t.price, t.expiry,
ROW_NUMBER() OVER (PARTITION BY p.id ORDER BY t.expiry) rn
FROM ports p
LEFT JOIN tariffs t ON t.portId = p.id
WHERE t.expiry > 1648594700
)
SELECT id, name, price, expiry
FROM cte
WHERE rn = 1
ORDER BY id;
This logic would return one record for each port having the nearest expiry.