MySql 选择和 SUM 问题

Question

大家早上好，

我的运动成绩 table 遇到了一些问题，我确信这些问题很简单，但我似乎无法理解为什么它们不是正在工作。

a) 仅选择 2014 赛季。

对于 a) 我假设它应该只是一个 WHERE Season = '2014'，但它抛出了：Warning: mysql_fetch_assoc() expects parameter 1 to be resource, boolean given in。我也试过 = 2014 因为 table 是一个整数，但得到相同的结果。

在我拔掉所有头发之前，非常感谢任何帮助！ :)

$result = mysql_query("
SELECT team
     , COUNT(*)  played
     , SUM(win)  wins
     , SUM(loss) lost
     , SUM(win)/count(*) pctWon1
     , SUM(draw) draws
     , SUM(SelfScore) ptsfor
     , SUM(OpponentScore) ptsagainst
     , SUM(SelfScore) - SUM(OpponentScore) goal_diff
     , SUM((win*2 + draw)- loss) score
     , SUM(win*2 + draw)/count(*) pctWon

FROM (
      SELECT team
     , SelfScore
     , OpponentScore
     , SelfScore > OpponentScore win
     , SelfScore < OpponentScore loss
     , SelfScore = OpponentScore draw
      FROM (
        SELECT HomeTeam team, HomeScore SelfScore, AwayScore OpponentScore
        FROM Game
        union all select AwayTeam, AwayScore, HomeScore
        FROM Game
       ) a
) b
WHERE Season = '2014'
GROUP BY team
ORDER BY pctWon DESC, score DESC, ptsagainst DESC;
        ");

Answer 1

您正在将 where 子句应用于外部查询 (b)，其中没有这样的列 Season。您应该将其移至内部查询：

$result = mysql_query("
SELECT team
     , COUNT(*)  played
     , SUM(win)  wins
     , SUM(loss) lost
     , SUM(win)/count(*) pctWon1
     , SUM(draw) draws
     , SUM(SelfScore) ptsfor
     , SUM(OpponentScore) ptsagainst
     , SUM(SelfScore) - SUM(OpponentScore) goal_diff
     , SUM((win*2 + draw)- loss) score
     , SUM(win*2 + draw)/count(*) pctWon

FROM (
      SELECT team
     , SelfScore
     , OpponentScore
     , SelfScore > OpponentScore win
     , SelfScore < OpponentScore loss
     , SelfScore = OpponentScore draw
      FROM (
        SELECT HomeTeam team, HomeScore SelfScore, AwayScore OpponentScore
        FROM Game
        WHERE Season = '2014'
        UNION ALL 
        SELECT AwayTeam, AwayScore, HomeScore
        FROM Game
        WHERE Season = '2014'
       ) a
) b
GROUP BY team
ORDER BY pctWon DESC, score DESC, ptsagainst DESC;
");

Answer 2

您所做的事情不需要两级子查询。（MySQL 实际上实现了子查询，这增加了性能开销。）。但是，如果你这样做，你应该从中提取你想要的所有字段。

我建议这样写查询：

SELECT team, COUNT(*)  played, SUM(IsWin) as wins, SUM(IsLoss) as losses,
       SUM(IsWin)/count(*) as pctWon1,
       SUM(Draw) as draws,
       SUM(SelfScore) as ptsfor, SUM(OpponentScore) as ptsagainst,
       SUM(SelfScore) - SUM(OpponentScore) as goal_diff,
       SUM((IsWin*2 + IsDraw) - IsLoss) as score,
       SUM(IsWin*2 + IsDraw) / count(*) pctWon
FROM (SELECT season, HomeTeam as team, HomeScore as SelfScore, AwayScore as OpponentScore,
             (HomeScore > AwayScore) as IsWin,
             (HomeScore < AwayScore) as IsLoss,
             (HomeScore = AwayScore) as IsDraw
      FROM Game
      UNION ALL
      SELECT Season, AwayTeam, AwayScore, HomeScore,
             (AwayScore > HomeScore) as IsWin,
             (AwayScore < HomeScore) as IsLoss,
             (AwayScore = HomeScore) as IsDraw
      FROM Game
     ) t
WHERE Season = 2014
GROUP BY team
ORDER BY pctWon DESC, score DESC, ptsagainst DESC;

我对重复标志的定义三遍并不感到兴奋。而且，在大多数数据库中，我更愿意在子查询中使用一次逻辑。 MySQL，但是，作为实际的性能损失，所以最好避免。

一个小建议：在定义列别名时使用as。这将帮助您在缺少逗号时发现错误。

MySql 选择和 SUM 问题

MySql Selection and SUM issues

mysql

sql

sum

division

where