SQL query joining a few tables (MySQL) - mysql

Question

I need a "little" help with an SQL query (MySQL).
I have the following tables:
COURIERS table:
+------------+
| COURIER_ID |
+------------+
DELIVERIES table:
+-------------+------------+------------+
| DELIVERY_ID | COURIER_ID | START_DATE |
+-------------+------------+------------+
ORDERS table:
+----------+-------------+-------------+
| ORDER_ID | DELIVERY_ID | FINISH_DATE |
+----------+-------------+-------------+
COORDINATES table:
+-------------+-----+-----+------+
| DELIVERY_ID | LAT | LNG | DATE |
+-------------+-----+-----+------+
In the real database I have more columns in each table, but for this example the above columns are enough.
What do I need?
An SQL query that returns all couriers [COURIER_ID], their last
delivery [DELIVERY_ID] (based on last START_DATE), the
delivery's last coordinate [LAT and LNG] (based on last DATE) and the remaining orders count (total of orders of the last delivery that have no FINISH_DATE).
A courier can have no deliveries, in this case I want DELIVERY_ID =
NULL, LAT = NULL and LNG = NULL in the result.
A delivery can have no coordinates, in this case I want LAT = NULL
and LNG = NULL in the result.
What was I able to do?
SELECT c.`COURIER_ID`,
d.`DELIVERY_ID`,
r.`LAT`,
r.`LNG`,
(SELECT COUNT(DISTINCT `ORDER_ID`)
FROM `ORDERS`
WHERE `DELIVERY_ID` = d.`DELIVERY_ID`
AND `FINISH_DATE` IS NULL) AS REMAINING_ORDERS
FROM `COURIERS` AS c
LEFT JOIN `DELIVERIES` AS d USING (`COURIER_ID`)
LEFT JOIN `COORDINATES` AS r ON r.`DELIVERY_ID` = d.`DELIVERY_ID`
WHERE (CASE WHEN
(SELECT MAX(`START_DATE`)
FROM `DELIVERIES`
WHERE `COURIER_ID` = c.`COURIER_ID`) IS NULL THEN d.`START_DATE` IS NULL ELSE d.`START_DATE` =
(SELECT MAX(`START_DATE`)
FROM `DELIVERIES`
WHERE `COURIER_ID` = c.`COURIER_ID`) END)
AND (CASE WHEN
(SELECT MAX(`DATE`)
FROM `COORDINATES`
WHERE `DELIVERY_ID` = d.`DELIVERY_ID`) IS NULL THEN r.`DATE` IS NULL ELSE r.`DATE` =
(SELECT MAX(`DATE`)
FROM `COORDINATES`
WHERE `DELIVERY_ID` = d.`DELIVERY_ID`) END)
GROUP BY c.`COURIER_ID`
ORDER BY d.`START_DATE` DESC
The problem is that this query is very slow (from 5 to 20 seconds) when I have over 5k COORDINATES and it does not returns all couriers sometimes.
Thank you so much for any solution.

Answer 1

Try this:
SELECT C.COURIER_ID, D.DELIVERY_ID, D.START_DATE, D.FINISH_DATE,
B.LAT, B.LNG, B.DATE, C.NoOfOrders
FROM COURIERS C
LEFT JOIN ( SELECT *
FROM (SELECT *
FROM DELIVERIES D
ORDER BY D.COURIER_ID, D.START_DATE DESC
) A
GROUP BY COURIER_ID
) AS A ON C.COURIER_ID = A.COURIER_ID
LEFT JOIN ( SELECT *
FROM (SELECT *
FROM COORDINATES CO
ORDER BY CO.DELIVERY_ID, CO.DATE DESC
) B
GROUP BY CO.DELIVERY_ID
) AS B ON A.DELIVERY_ID = B.DELIVERY_ID
LEFT JOIN ( SELECT O.DELIVERY_ID, COUNT(1) NoOfOrders
FROM ORDERS O WHERE FINISH_DATE IS NULL
GROUP BY O.DELIVERY_ID
) AS C ON A.DELIVERY_ID = C.DELIVERY_ID;

Answer 2

I haven't been able to test this query since I don't have a mysql database set up right now, much less with this schema and sample data. But I think this will work for you:
select
c.courier_id
, d.delivery_id
, co.lat
, co.lng
, oc.cnt as remaining_orders
from
couriers c
left join (
select
d.delivery_id
, d.courier_id
from
deliveries d
inner join (
select
d.delivery_id
, max(d.start_date) as start_date
from
deliveries d
group by
d.delivery_id
) dmax on dmax.delivery_id = d.delivery_id and dmax.start_date = d.start_date
) d on d.courier_id = c.courier_id
left join (
select
c.delivery_id
, c.lat
, c.lng
from
coordinates c
inner join (
select
c.delivery_id
, max(c.date) as date
from
coordinates c
group by
c.delivery_id
) cmax on cmax.delivery_id = c.delivery_id and cmax.date = c.date
) co on co.delivery_id = d.delivery_id
left join (
select
o.delivery_id
, count(o.order_id) as cnt
from
orders o
where
o.finish_date is null
group by
o.delivery_id
) oc on oc.delivery_id = d.delivery_id