SELECT SUM - SQL 查询不起作用

Question

我创建了一个基于 Olympics 的小型数据库，用于运行一些 sql 查询。我正在尝试生成一个表格，显示每个国家/地区的名称以及来自这些国家/地区的运动员获得的金牌、银牌和铜牌总数。这是我的关系模型视图的屏幕截图：

Relational Model View

这是我正在尝试运行的查询：

<h1>Olympics Database</h1>
<h3>Summary Information</h3>

    <h4>Number of Olympic Athletes from United Kingdom</h4>

<?php

    $conn = mysqli_connect('localhost', '#####', '#####') or die ('Could not connect:' . mysqli_error($conn));
    echo 'Successfully Connected. <br/>';

    mysqli_select_db($conn, '#####') or die('Database will not open');
    echo 'Database Connected. <br/> <br/>';

    $query2 = 'SELECT CountryAbbrev, (SELECT COUNT(CountryAbbrev) FROM athlete WHERE MedalID = 401 AND ath.CountryAbbrev = athlete.CountryAbbrev) AS Gold, (SELECT COUNT(CountryAbbrev) FROM athlete WHERE MedalID = 402 AND ath.CountryAbbrev = athlete.CountryAbbrev) AS Silver, (SELECT COUNT(CountryAbbrev) FROM athlete WHERE MedalID = 403 AND ath.CountryAbbrev = athlete.CountryAbbrev) AS Bronze FROM athlete AS ath';
    $result2 = mysqli_query($conn, $query2) or die ('Invalid Query');

    echo'<table><tr><th>Country Name</th><th>Gold</th><th>Silver</th><th>Bronze</th></tr>';
    $row = mysqli_fetch_row($result2);
    echo'<tr><td>' .$row[0].'</td><td>' .$row[1].'</td><td>' .$row[2].'</td><td>' .$row[3].'</td></tr>';
    echo'</table>';

    mysqli_close($conn);
    ?>

我得到的只是无效的查询。根据我的关系模型视图，谁能帮我弄清楚如何在一张桌子上显示每个国家获得的金牌、银牌和铜牌的总数？

更新： 这是输出的屏幕截图：

Answer 1

由于您在表中选择了未定义的字段，您的原始 SQL 查询返回无效查询。即athlete 表没有名为MedalName 的字段。

您可以使用以下 SQL 查询，通过了解每种奖牌类型的 id，我假设它们分别是 Gold、Silver 和 Bronze 的 1、2、3。

SELECT CountryAbbrev,
 (SELECT COUNT(CountryAbbrev) FROM athlete WHERE MedalID = 1 AND ath.CountryAbbrev = athlete.CountryAbbrev) AS Gold, 
(SELECT COUNT(CountryAbbrev) FROM athlete WHERE MedalID = 2 AND ath.CountryAbbrev = athlete.CountryAbbrev) AS Silver, 
(SELECT COUNT(CountryAbbrev) FROM athlete WHERE MedalID = 3 AND ath.CountryAbbrev = athlete.CountryAbbrev) AS Bronze 
FROM athlete AS ath

更新

抱歉，应该是 COUNT 而不是 SUM。查看SUM 和COUNT from this link 之间的区别

Answer 2

试试这个

SELECT c.CountryAbbrev, 
    (select count(a.MedalID) FROM athlete a WHERE c.CountryAbbrev=a.CountryAbbrev and a.MedalName = "Gold" ) as gold,
    (select count(a.MedalID) FROM athlete a WHERE c.CountryAbbrev=a.CountryAbbrev and a.MedalName = "Silver" ) as Silver,
    (select count(a.MedalID) FROM athlete a WHERE c.CountryAbbrev=a.CountryAbbrev and a.MedalName = "Bronze" ) as Bronze
from country as c 

Answer 3

为了修复“无效查询”，您需要与medal 表进行左连接，将ANDs 更改为ORs，并使用group by 子句。此外，由于您需要奖牌数，因此您需要将SUM 替换为COUNT。所以你可以这样做：

SELECT CountryAbbrev as country, count(athlete.MedalID) 
FROM athlete 
  LEFT JOIN medal on medal.MedalID = athlete.MedalID
WHERE MedalName = "Gold" 
  OR MedalName = "Silver" 
  OR MedalName = "Bronze"
GROUP BY CountryAbbrev;

此查询输出每个国家/地区的奖牌总数（# 金 + # 银 + # 铜）：

+---------+------------------------+
| country | count(athlete.MedalID) |
+---------+------------------------+
| AU      |                      4 |
| US      |                      5 |
+---------+------------------------+

如果你想在不同的列中分别打印出金、银、铜的数量，那么你可以使用以下查询：

SELECT CountryAbbrev as country, 
  sum(if(MedalName = "Gold", 1, 0)) as Gold, 
  sum(if(MedalName = "Silver", 1, 0)) as Silver, 
  sum(if(MedalName = "Bronze", 1, 0)) as Bronze 
FROM athlete 
  LEFT JOIN medal on medal.MedalID = athlete.MedalID 
WHERE MedalName = "Gold" 
  OR MedalName = "Silver" 
  OR MedalName = "Bronze" 
GROUP BY CountryAbbrev;

此查询将输出如下内容：

+---------+------+--------+--------+
| country | Gold | Silver | Bronze |
+---------+------+--------+--------+
| AU      |    1 |      2 |      1 |
| US      |    2 |      1 |      2 |
+---------+------+--------+--------+

如果您还想添加总计列，请尝试以下查询：

SELECT CountryAbbrev as country, 
  sum(if(MedalName = "Gold", 1, 0)) as Gold, 
  sum(if(MedalName = "Silver", 1, 0)) as Silver, 
  sum(if(MedalName = "Bronze", 1, 0)) as Bronze, 
  count(MedalName) as Total 
FROM athlete 
  LEFT JOIN medal on medal.MedalID = athlete.MedalID 
WHERE MedalName = "Gold" 
  OR MedalName = "Silver" 
  OR MedalName = "Bronze" 
GROUP BY CountryAbbrev;

此查询将输出：

+---------+------+--------+--------+-------+
| country | Gold | Silver | Bronze | Total |
+---------+------+--------+--------+-------+
| AU      |    1 |      2 |      1 |     4 |
| US      |    2 |      1 |      2 |     5 |
+---------+------+--------+--------+-------+

我已经在我的机器上运行了这些查询，它们按预期工作。