SQL query joining a few tables (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