我有两张桌子:
奥林匹克运动员,栏目为gold_country,silver_country,bronze_country
国家/地区列标志
我想相应地列出奥运奖牌榜。我有这个查询,它的工作原理,但似乎杀了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)
结果将如下:
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`)
答案 0 :(得分:0)
这比您在交叉连接关系中为每一行执行三个不同SELECT
子查询的当前解决方案更有效(并且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,不是在每个金色,银色和铜色列中存储实际的文本国家名称,只需存储基于整数的国家/地区id
。对整数的比较总是比对字符串的比较更快。
此外,一旦将olympic_medalists
表中的每个国家/地区名称替换为相应的ID,您就需要在每个列(金,银和铜牌)上创建索引。
将文本名称更新为相应的id
是一项简单的任务,可以使用单个UPDATE
语句和一些ALTER TABLE
命令来完成。
答案 1 :(得分:0)
试试这个:
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