Question

我正在尝试为高尔夫数据库编写查询。它需要返回statisticID = 1 p2sStatistic > 65且statisticID = 3 p2sStatistic > 295 {。}}的玩家。一个statisticID是驾驶距离，另一个是精确度等等。我尝试了以下但是它不起作用，似乎无法在线找到答案。如果不进行观察，我该怎么做呢？

SELECT playerFirstName, playerLastName
FROM player2Statistic, player 
WHERE player.playerID=player2Statistic.playerID
AND player2Statistic.statisticID=statistic.statisticID
AND p2sStatistic.3 > 295
AND p2sStatistic.1 > 65;

http://i.imgur.com/o8epk.png - db的图片

尝试获取它只输出满足这两个条件的玩家列表。

Answer 1

您缺少查询中的statistic表。您需要根据where条款加入。

您还需要使用正确的连接语法。

以下版本在统计表中连接两次，一次为“1”，一次为“3”：

SELECT distinct playerFirstName, playerLastName
FROM player2Statistic p2s join
     player p
     on p.playerId = p2s.playerId join
     statistic s3
     on s3.StatisticId = p2s.statistcId and
        s3.StatisticId = 3 join
     statistic s1
     on s1.StatisticId = p2s.statisticId and
        s1.StatisticId = 1
WHERE  (s3.statistic > 295 and s1.statistic > 65)

Answer 2

您需要两次加入统计信息表：

SELECT playerFirstName, playerLastName
  FROM player p
  JOIN player2Statistic s1
    on p.playerID=s1.playerID and s1.statisticID = 1
  JOIN player2Statistic s3
    on p.playerID=s3.playerID and s1.statisticID = 3
 WHERE s1.p2sStatistic > 65 and s3.p2sStatistic > 295;

Answer 3

对于没有重复的的玩家列表，EXISTS半连接可能是最好的：

SELECT playerFirstName, playerLastName
FROM   player AS p 
WHERE EXISTS (
   SELECT 1
   FROM   player2Statistic AS ps 
   WHERE  ps.playerID = p.playerID
   AND    ps.StatisticID = 1
   AND    ps.p2sStatistic > 65
   )
AND EXISTS (
   SELECT 1
   FROM   player2Statistic AS ps 
   WHERE  ps.playerID = p.playerID
   AND    ps.StatisticID = 3
   AND    ps.p2sStatistic > 295
   );

列名称和上下文源自提供的屏幕截图。问题中的查询并未完全覆盖它注意括号，它们需要处理运算符优先级。

这可能更快（重复可能不可能）：

SELECT p.playerFirstName, p.playerLastName
FROM   player           AS p 
JOIN   player2Statistic AS ps1 USING (playerID)
JOIN   player2Statistic AS ps3 USING (playerID)
AND    ps1.StatisticID = 1
AND    ps1.p2sStatistic > 65
AND    ps3.StatisticID = 3
AND    ps3.p2sStatistic > 295;

如果您的绝密品牌RDBMS不支持SQL标准(USING (playerID)，请将ON ps1.playerID = p.playerID替换为相同的效果。

这是关系划分的情况。在此相关问题下，找到许多更多查询技术来处理它：
How to filter SQL results in a has-many-through relation

使用不同的值查询不同的ID？

3 个答案: