1

我有 2 张桌子：

  1. Olympic_medalists 与列 gold_country、silver_country、bronze_country

  2. 带有国家列的标志

我想相应地列出奥运奖牌表。我有这个查询，它有效，但它似乎杀死了 mysql。希望有人可以帮助我优化查询。

SELECT DISTINCT country AS sc,
    IFNULL(
        (SELECT COUNT(silver_country) 
            FROM olympic_medalists 
        WHERE silver_country = sc AND silver_country != '' 
        GROUP BY silver_country),0) AS silver_medals, 
    IFNULL(
        (SELECT COUNT(gold_country) 
            FROM olympic_medalists 
        WHERE gold_country = sc AND gold_country != '' 
        GROUP BY gold_country),0) AS gold_medals,
    IFNULL(
        (SELECT COUNT(bronze_country) 
            FROM olympic_medalists 
        WHERE bronze_country = sc AND bronze_country != '' 
        GROUP BY bronze_country),0) AS bronze_medals
FROM olympic_medalists, flags 
GROUP BY country, gold_medals, silver_country, bronze_medals HAVING (
    silver_medals >= 1 || gold_medals >= 1 || bronze_medals >= 1)
ORDER BY gold_medals DESC, silver_medals DESC, bronze_medals DESC,   
SUM(gold_medals+silver_medals+bronze_medals)

结果将是：

country  |  g  |  s  |  b  |  tot
---------------------------------
country1 |  9  |  5  |  2  |  16
country2 |  5  |  5  |  5  |  15

等等

谢谢！

olympic medalists:

  `id` int(8) NOT NULL auto_increment,
  `gold_country` varchar(64) collate utf8_unicode_ci default NULL,
  `silver_country` varchar(64) collate utf8_unicode_ci default NULL,
  `bronze_country` varchar(64) collate utf8_unicode_ci default NULL, PRIMARY KEY  (`id`)

flags

  `id` int(11) NOT NULL auto_increment,
  `country` varchar(128) default NULL,
  PRIMARY KEY  (`id`)
4

2 回答 2

0

这将比您当前SELECT为交叉连接关系中的每一行执行三个不同子查询的解决方案高效得多（您想知道为什么它会停止！）：

SELECT    a.country,
          COALESCE(b.cnt,0)     AS g,
          COALESCE(c.cnt,0)     AS s,
          COALESCE(d.cnt,0)     AS b,
          COALESCE(b.cnt,0) +
          COALESCE(c.cnt,0) +
          COALESCE(d.cnt,0)     AS tot
FROM      flags a
LEFT JOIN (
          SELECT   gold_country, COUNT(*) AS cnt 
          FROM     olympic_medalists 
          GROUP BY gold_country
          ) b ON a.country = b.gold_country
LEFT JOIN (
          SELECT   silver_country, COUNT(*) AS cnt 
          FROM     olympic_medalists 
          GROUP BY silver_country
          ) c ON a.country = c.silver_country
LEFT JOIN (
          SELECT   bronze_country, COUNT(*) AS cnt 
          FROM     olympic_medalists 
          GROUP BY bronze_country
          ) d ON a.country = d.bronze_country

更快的是，不是在金、银和青铜列中存储实际的文本国家名称，而是存储基于整数的国家id。整数比较总是比字符串比较快。

此外，一旦您将olympic_medalists表中的每个国家/地区名称替换为相应的 id，您将希望在每列（金、银和青铜）上创建一个索引。

将文本名称更新为它们对应id的 's 是一项简单的任务，可以通过单个UPDATE语句和一些ALTER TABLE命令来完成。

于 2012-08-04T06:27:59.017 回答
0

尝试这个：

SELECT F.COUNTRY,IFNULL(B.G,0) AS G,IFNULL(B.S,0) AS S,
IFNULL(B.B,0) AS B,IFNULL(B.G+B.S+B.B,0) AS TOTAL
FROM FLAGS F LEFT OUTER JOIN
      (SELECT A.COUNTRY,
         SUM(CASE WHEN MEDAL ='G' THEN 1 ELSE 0 END) AS G,
         SUM(CASE WHEN MEDAL ='S' THEN 1 ELSE 0 END) AS S,
         SUM(CASE WHEN MEDAL ='B' THEN 1 ELSE 0 END) AS B
      FROM   
          (SELECT GOLD_COUNTRY AS COUNTRY,'G' AS MEDAL 
           FROM OLYMPIC_MEDALISTS WHERE GOLD_COUNTRY IS NOT NULL
           UNION ALL
           SELECT SILVER_COUNTRY AS COUNTRY,'S' AS MEDAL 
           FROM OLYMPIC_MEDALISTS WHERE SILVER_COUNTRY IS NOT NULL
           UNION ALL
           SELECT BRONZE_COUNTRY AS COUNTRY,'B' AS MEDAL 
           FROM OLYMPIC_MEDALISTS WHERE BRONZE_COUNTRY IS NOT NULL)A
      GROUP BY A.COUNTRY)B
 ON F.COUNTRY=B.COUNTRY
 ORDER BY IFNULL(B.G,0) DESC,IFNULL(B.S,0) DESC,
          IFNULL(B.B,0) DESC,IFNULL(B.G+B.S+B.B,0) DESC,F.COUNTRY
于 2012-08-04T06:36:20.083 回答