优化 MySQL 慢查询答案

【问题标题】：Optimise slow MySQL Query优化 MySQL 慢查询
【发布时间】：2013-12-13 07:32:40
【问题描述】：

我正在使用 MySQL，但此查询存在一些性能问题：

 SELECT s.ID, headline, uId, teaser, hide_image_archiv, image, image_caption, date_format(cDate, '%d.%m.%Y | %H:%i Uhr') as date, channelid, channel_article.name FROM
        (SELECT article.ID, uId, headline, teaser, cDate, image, image_caption, channelid, hide_image_archiv
 FROM article
        inner join article_cCountry on article.ID = ID1 and ID2 = 1
 WHERE sDate < now()
        and (eDate > now() or eDate = 0)
        and released = 'TRUE'
        and (uId in (select ID from user where released = 1) or uId = 0)
 ORDER BY cDate DESC) AS s, channel_article where channelid = channel_article.ID AND channelid = 8 order by cDate desc LIMIT 3

解释：

大约需要 0.30 - 0.40 秒

有什么办法可以优化吗？

【问题讨论】：

标签： php mysql database query-optimization

【解决方案1】：

查询：

SELECT article.ID,
          uId,
          headline,
          teaser,
          cDate,
          image,
          image_caption,
          channelid,
          hide_image_archiv,
          channel_article.name
   FROM article
   INNER JOIN article_cCountry ON article.ID = ID1
    AND ID2 = 1
   INNER JOIN channel_article
    ON channelid = channel_article.ID
    AND channelid = 8
   WHERE sDate < now()
     AND (eDate > now()
          OR eDate = 0)
     AND released = 'TRUE'
     AND (uId IN
            (SELECT ID
             FROM USER
             WHERE released = 1)
          OR uId = 0)
   ORDER BY cDate DESC LIMIT 3

【讨论】：

惊人的 ;) 0.0019 秒
我用“AND channelid != 8”而不是“AND channelid = 8”尝试了另一个查询（0.3 秒而不是 0.0019）为什么 != 比 = 慢？

【解决方案2】：

你可以试试这个，

SELECT *
FROM
(
SELECT s.ID, headline, uId, teaser, hide_image_archiv, image, image_caption, date_format(cDate, '%d.%m.%Y | %H:%i Uhr') as date, channelid, channel_A.name, 
case when eDate = 0 the 1 when eDate > now() then 1 else 0 end as FILTER_IND1,
CASE WHEN sDate < now() THEN 1 ELSE 0 END AS FILTER_IND2
FROM article
inner join article_cCountry on article.ID = ID1 and ID2 = 1 AND released = 'TRUE' AND CHANNELID = 8
INNER JOIN 
(
    SELECT 0 FROM DUAL
    UNION 
    SELECT ID FROM USER WHERE RELEASED = 1 
) AS U
ON U.ID = UID
INNER JOIN CHANNEL_ARTICLE AS A 
ON A.ID = CHANNELID
) A
WHERE FILTER_IND = 1
ORDER BY CDATE DESC
LIMIT 3

【讨论】：