最大/最小/计数等没有给出好的价值

Question

我有一个来自 ergast.com 的 f1 database。我试图在每场比赛中为每个车手获得最好的laptime 和pitstops 的数量，所以我编写了这样的 sql 查询：

SELECT results.driverId, results.constructorId, races.circuitId, races."year"-1949,
       results.statusId, results.positionOrder, results.grid, results.points, 
       results.laps, ISNULL(max(pitstops.stop), 0), min(laptimes.milliseconds), 
       results.fastestLapTime, drivers.forename, drivers.surname, circuits.name
FROM results 
INNER JOIN races 
   ON (results.raceId = races.raceId)
LEFT OUTER JOIN pitstops 
   ON (races.raceId = pitstops.raceId)
LEFT OUTER JOIN laptimes 
   ON (laptimes.raceId = races.raceId)
INNER JOIN drivers 
   ON (drivers.driverId = results.driverId)
INNER JOIN circuits 
   ON (circuits.circuitId = races.circuitId)
WHERE ((races."year"=2011) OR (races."year"=2012))
  AND ((races.circuitId = 1) OR (races.circuitId = 2))
GROUP BY results.driverId, constructorId, races.circuitId, races."year"-1949,
         statusId, positionOrder, grid, points, laps, fastestLapTime, forename,
         surname, circuits.name

不幸的是，对于给定比赛的每位车手，这给了我相同的最佳 laptime 和 pitstops 数量。我该如何解决？我应该在group by 中添加一些内容吗？

Answer 1

您仅在raceId 上加入进站，从而获得每场比赛的最大进站。但是您会说“以及给定比赛中每位车手的进站次数”。这表明进站应该与车手相关，例如：

LEFT OUTER JOIN pitstops 
   ON (results.raceId = pitstops.raceId and results.driverId = pitstops.driverId)

单圈时间也是如此。

（您的查询中可能有更多错误。如果您需要更多帮助，请使用表名限定所有列，以便我们查看哪些列在哪个表中。最好是表定义。）

Answer 2

这是另一个“答案”:-)

您正在使用技术 ID（raceId、driverId 等），但您很惊讶必须加入多个列。对于基于技术 ID 的数据库，这确实有点不典型。那么让我们来看看为什么会这样......

应该有一个表格列出每场比赛的车手。我们就叫它participation：

participation(participationid, raceid, driverid)

有了这样一个表，您的其他表将不再包含raceid 和driverid 的组合，而只包含participationid：

pitstops(pitstopid, participationid, stop, ...)

laptimes(laptimeid, participationid, milliseconds, ...)

results(resultid, participationid, points, ...)

您只需要相应地加入该列：

LEFT OUTER JOIN pitstops 
  ON pitstops.participationid = results.participationid

不过，我认为每个raceid 和driverid 只能有一个结果记录？那么您的参与表实际上就是结果表（只是名称更差:-)。因此，您应该在表和引用它的其他表中有一个 resultid：

pitstops(pitstopid, resultid, stop, ...)

laptimes(laptimeid, resultid, milliseconds, ...)

您只需要相应地加入该列：

LEFT OUTER JOIN pitstops 
  ON pitstops.resultid = results.resultid

Answer 3

添加到已经给出的答案：您可以通过获取子查询中的聚合来简化查询（在FROM 子句或SELECT 子句中）。例如：

select 
  results.driverid,
  results.constructorid,
  races.circuitid,
  races."year" - 1949,
  results.statusid,
  results.positionorder,
  results.grid,
  results.points,
  results.laps,
  (
    select coalesce(max(stop), 0)
    from pitstops
    where pitstops.raceid = results.raceid
    and pitstops.driverid = results.driverid
  ) as max_pitstops,
  (
    select coalesce(min(milliseconds), 0)
    from laptimes
    where laptimes.raceid = results.raceid
    and laptimes.driverid = results.driverid
  ) as min_laptimes,
  results.fastestlaptime,
  drivers.forename,
  drivers.surname,
  circuits.name
from results
join drivers on drivers.driverid = results.driverid
join races on races.raceid = results.raceid
join circuits on circuits.circuitid = races.circuitid
where races."year" in (2011, 2012)
and races.circuitid in (1, 2);

或

select 
  results.driverid,
  results.constructorid,
  races.circuitid,
  races."year" - 1949,
  results.statusid,
  results.positionorder,
  results.grid,
  results.points,
  results.laps,
  coalesce(pits.max_stop, 0) as max_pitstops,
  coalesce(laps.min_milliseconds, 0) as min_laptimes,
  results.fastestlaptime,
  drivers.forename,
  drivers.surname,
  circuits.name
from results
join drivers on drivers.driverid = results.driverid
join races on races.raceid = results.raceid
join circuits on circuits.circuitid = races.circuitid
left join
(
  select raceid, driverid, max(stop) as max_stop
  from pitstops
  group by raceid, driverid
) pits on pits.raceid = results.raceid and pits.driverid = results.driverid
left join
(
  select raceid, driverid, min(milliseconds) as min_milliseconds
  from laptimes
  group by raceid, driverid
) laps on laps.raceid = results.raceid and laps.driverid = results.driverid
where races."year" in (2011, 2012)
and races.circuitid in (1, 2);