加入几个表的SQL查询（MySQL）

Question

我需要SQL查询（MySQL）的“小”帮助。

我有以下表格：

COURIERS表：

+------------+ 
    | COURIER_ID | 
    +------------+ 

DELIVERIES表：

+-------------+------------+------------+ 
    | DELIVERY_ID | COURIER_ID | START_DATE | 
    +-------------+------------+------------+ 

ORDERS表：

+----------+-------------+-------------+ 
    | ORDER_ID | DELIVERY_ID | FINISH_DATE | 
    +----------+-------------+-------------+ 

COORDINATES表：

+-------------+-----+-----+------+ 
    | DELIVERY_ID | LAT | LNG | DATE | 
    +-------------+-----+-----+------+ 

在真实的数据库我在每个表中的列多，但在本例以上列是不够的。

我需要什么？

• 一个SQL查询，返回所有快递公司的[COURIER_ID]，他们最后 交运[DELIVERY_ID（基于最后START_DATE），该 交付的最后一个坐标[LAT和LNG]（基于最后DATE）和剩余订单数量（没有FINISH_DATE的最后一次交货的订单总数）。

• 快递员可以没有交付，在这种情况下，我想DELIVERY_ID = NULL ，LAT = NULL和结果LNG = NULL。

• 一个投递可以没有坐标，在这种情况下，我想要LAT = NULL 和LNG = NULL结果。

我能做什么？

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 

的问题是，这个查询是很慢的（5〜20秒）时，我有过5K COORDINATES，它有时不返回所有快递员。

非常感谢你的解决方案。

Answer 1

我一直无法与该模式和样本数据来检验这个查询，因为我没有一个MySQL数据库建立，现在做的，要少得多。但我认为这将适用于你：

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 

Answer 2

试试这个：

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;