Select MySQL 中多列的 MAX()

Question

我目前有大量查询（使用 PHP 和 MySQL），我不确定如何优化它以减少其 18-25 秒的大量负载。我查看了以前的答案，发现他们都编写了类似的大量代码，导致类似的脚本执行时间，所以我想看看是否有人有任何替代想法而不是已经存在的想法构成：

TLDR; 我需要 select 每个分析 ID 的最大列，这会带来巨大的负载，所以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";

这是从大量 table 中获取数据，所以我不希望它花费 0 秒，但是任何时间减少都可以，而不是 ~21 秒。

Answer 1

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

Answer 2

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。这可能会更好：

INDEX(bid, ip, country_code, country)

Select MySQL 中多列的 MAX()

Select MAX() of Multiple Columns in MySQL

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