我有一个非常大的表(~1 000 000 行)和带有联合、连接和 where 语句的复杂查询(用户可以选择不同的 ORDER BY 列和方向)。我需要获取分页的行数。如果我运行查询而不计算行数,它会很快完成。如何以最快的方式实现分页? 我尝试使用 EXPLAIN SELECT 和 SHOW TABLE STATUS 来获取近似行数,但它与实际行数有很大不同。 我的查询如下(简化):
SELECT * FROM (
(
SELECT * FROM table_1
LEFT JOIN `table_a` ON table_1.record_id = table_a.id
LEFT JOIN `table_b` ON table_a.id = table_b.record_id
WHERE table_1.a > 10 AND table_a.b < 500 AND table_b.c = 1
ORDER BY x ASC
LIMIT 0, 10
)
UNION
(
SELECT * FROM table_2
LEFT JOIN `table_a` ON table_2.record_id = table_a.id
LEFT JOIN `table_b` ON table_a.id = table_b.record_id
WHERE table_2.d < 10 AND table_a.e > 500 AND table_b.f = 1
ORDER BY x ASC
LIMIT 0, 10
)
) tbl ORDER BY x ASC LIMIT 0, 10
无限制的查询结果约为~100 000行,如何以最快的方式获得这个近似计数? 我的生产查询示例如下:
SELECT SQL_CALC_FOUND_ROWS * FROM (
(
SELECT
articles_log.id AS log_id, articles_log.source_table,
articles_log.record_id AS id, articles_log.dat AS view_dat,
articles_log.lang AS view_lang, '1' AS view_count, '1' AS unique_view_count,
articles_log.user_agent, articles_log.ref, articles_log.ip,
articles_log.ses_id, articles_log.bot, articles_log.source_type, articles_log.link,
articles_log.user_country, articles_log.user_platform,
articles_log.user_os, articles_log.user_browser,
`contents`.dat AS source_dat, `contents_trans`.header, `contents_trans`.custom_text
FROM articles_log
INNER JOIN `contents` ON articles_log.record_id = `contents`.id
AND articles_log.source_table = 'contents'
INNER JOIN `contents_trans` ON `contents`.id = `contents_trans`.record_id
AND `contents_trans`.lang='lv'
WHERE articles_log.dat > 0
AND articles_log.dat >= 1488319200
AND articles_log.dat <= 1489355999
AND articles_log.bot = '0'
AND (articles_log.record_id NOT LIKE '%\_404' AND articles_log.record_id <> '404'
OR articles_log.source_table <> 'contents')
)
UNION
(
SELECT
articles_log.id AS log_id, articles_log.source_table,
articles_log.record_id AS id, articles_log.dat AS view_dat,
articles_log.lang AS view_lang, '1' AS view_count, '1' AS unique_view_count,
articles_log.user_agent, articles_log.ref, articles_log.ip,
articles_log.ses_id, articles_log.bot,
articles_log.source_type, articles_log.link,
articles_log.user_country, articles_log.user_platform,
articles_log.user_os, articles_log.user_browser,
`news`.dat AS source_dat, `news_trans`.header, `news_trans`.custom_text
FROM articles_log
INNER JOIN `news` ON articles_log.record_id = `news`.id
AND articles_log.source_table = 'news'
INNER JOIN `news_trans` ON `news`.id = `news_trans`.record_id
AND `news_trans`.lang='lv'
WHERE articles_log.dat > 0
AND articles_log.dat >= 1488319200
AND articles_log.dat <= 1489355999
AND articles_log.bot = '0'
AND (articles_log.record_id NOT LIKE '%\_404' AND articles_log.record_id <> '404'
OR articles_log.source_table <> 'contents')
)
) tbl ORDER BY view_dat ASC LIMIT 0, 10
非常感谢!
最佳答案
如果你可以使用UNION ALL
而不是UNION
(这是 UNION DISTINCT
的快捷方式) - 换句话说 - 如果您不需要删除重复项,您可以尝试添加两个子查询的计数:
SELECT
(
SELECT COUNT(*) FROM table_1
LEFT JOIN `table_a` ON table_1.record_id = table_a.id
LEFT JOIN `table_b` ON table_a.id = table_b.record_id
WHERE table_1.a > 10 AND table_a.b < 500 AND table_b.c = 1
)
+
(
SELECT COUNT(*) FROM table_2
LEFT JOIN `table_a` ON table_2.record_id = table_a.id
LEFT JOIN `table_b` ON table_a.id = table_b.record_id
WHERE table_2.d < 10 AND table_a.e > 500 AND table_b.f = 1
)
AS cnt
没有ORDER BY
并且没有UNION
引擎可能不需要创建一个巨大的临时表。
更新
对于您的原始查询,请尝试以下操作:
- 仅选择
count(*)
. - 删除
OR articles_log.source_table <> 'contents'
从第一部分(内容)开始,因为我们知道这不是真的。 - 删除
AND (articles_log.record_id NOT LIKE '%\_404' AND articles_log.record_id <> '404' OR articles_log.source_table <> 'contents')
从第二部分(新闻)开始,因为我们知道这总是正确的,因为OR articles_log.source_table <> 'contents'
永远是真的。 - 删除
contents
的连接和news
。您可以加入*_trans
直接使用record_id
表 - 删除
articles_log.dat > 0
因为它与articles_log.dat >= 1488319200
是多余的
结果查询:
SELECT (
SELECT COUNT(*)
FROM articles_log
INNER JOIN `contents_trans`
ON `contents_trans`.record_id = articles_log.record_id
AND `contents_trans`.lang='lv'
WHERE articles_log.bot = '0'
AND articles_log.dat >= 1488319200
AND articles_log.dat <= 1489355999
AND articles_log.record_id NOT LIKE '%\_404'
AND articles_log.record_id <> '404'
) + (
SELECT COUNT(*)
FROM articles_log
INNER JOIN `news_trans`
ON `news_trans`.record_id = articles_log.record_id
AND `news_trans`.lang='lv'
WHERE articles_log.bot = '0'
AND articles_log.dat >= 1488319200
AND articles_log.dat <= 1489355999
) AS cnt
尝试以下索引组合:
articles_log(bot, dat, record_id)
contents_trans(lang, record_id)
news_trans(lang, record_id)
或
contents_trans(lang, record_id)
news_trans(lang, record_id)
articles_log(record_id, bot, dat)
这取决于数据,哪种组合更好。
我可能还有一点是错的,因为我不知道你的数据和业务逻辑。如果是这样,请尝试调整其他。
关于MySQL 行数,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/42747271/