选择MySQL中多列的MAX（）

Question

我目前有一个庞大的查询（使用PHP和MySQL），但不确定如何优化它以减少18-25秒的庞大负载。 我查看了以前的答案，发现它们都编写了大量类似的代码，从而导致相似的脚本执行时间，因此，我想看看是否有人会提出替代方案，而不是已经提出的方案构成：

TLDR; 我需要为每个分析ID选择最大列，这会承受巨大的负担，因此我需要以某种方式减少它

$qry = "SELECT DISTINCT ip,country_code,country,
(SELECT MAX(region)  FROM analytics RegOne WHERE bid='$id' AND RegOne.ip= IPOne.ip) AS region,
(SELECT MAX(city)    FROM analytics CitOne WHERE bid='$id' AND CitOne.ip= IPOne.ip) AS city,
(SELECT MAX(os)      FROM analytics OSOne  WHERE bid='$id' AND OSOne.ip= IPOne.ip) AS os,
(SELECT MIN(browser) FROM analytics BroOne WHERE bid='$id' AND BroOne.ip= IPOne.ip) AS browser,
(SELECT MIN(resolution) FROM analytics ResOne  WHERE bid='$id' AND ResOne.ip= IPOne.ip) AS resolution,
(SELECT MAX(timestamp)  FROM analytics DateOne WHERE bid='$id' AND DateOne.ip= IPOne.ip) AS LatestDate
FROM analytics AS IPOne
WHERE bid='$id'
ORDER BY LatestDate DESC
LIMIT 15 OFFSET $offset";

这是从一个巨大的表中获取数据，因此我不希望它花费0秒，但是任何时间减少都是可以的，而不是大约21秒。

Answer 1

为什么不

SELECT ip, country_code, country,
     MAX(region) as region,
     MAX...
     MAX(timestamp) as LatestDate
FROM analytics
WHERE bid = '$id'
GROUP BY ip, country_code, country
ORDER BY LatestDate DESC
LIMIT 15 OFFSET $offset";

您应该有一些以bid开头的索引。 这可能更好：

INDEX(bid, ip, country_code, country)

Answer 2

您应该在(bid, ip)上有一个复合键。 如果您在(bid)上有KEY，则添加（或替换为） (bid, ip)