几个星期前运行它时花了不到1分钟的查询现在花了10多分钟，看不到尽头。
新查询（需要很长时间）
select sds.school_id,
detail.year,
detail.race,
ROUND((detail.count / summary.total) * 100 ,2) as percent
FROM school_data_race_ethnicity_raw as detail
inner join school_data_schools as sds USING (school_id)
inner join (
select sds2.district_id, year, sum(count) as total
from school_data_race_ethnicity_raw
inner join school_data_schools as sds2 USING (school_id)
group by sds2.district_id, year
) as summary on summary.district_id = sds.district_id
and summary.year = detail.year
查询：
INSERT INTO school_data_race_ethnicity_schools (school_id, year, race, percent) (
SELECT school_id,
year,
race,
ROUND((count/(
SELECT SUM(count)
FROM school_data_race_ethnicity_raw as school_data_race_ethnicity_raw_inner
WHERE school_id = school_data_race_ethnicity_raw_outer.school_id
and year = school_data_race_ethnicity_raw_outer.year)
) * 100,2) as percent
FROM school_data_race_ethnicity_raw as school_data_race_ethnicity_raw_outer)
说明：
mysql> explain SELECT school_id,year,race,ROUND((count/(SELECT SUM(count)
-> FROM school_data_race_ethnicity_raw as school_data_race_ethnicity_raw_inner
-> WHERE
-> school_id = school_data_race_ethnicity_raw_outer.school_id and
-> year = school_data_race_ethnicity_raw_outer.year)) * 100,2) as percent
-> FROM school_data_race_ethnicity_raw as school_data_race_ethnicity_raw_outer;
+----+--------------------+--------------------------------------+------+----------------------------+------+---------+-----------------------------------------------------------------+-------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+--------------------+--------------------------------------+------+----------------------------+------+---------+-----------------------------------------------------------------+-------+-------------+
| 1 | PRIMARY | school_data_race_ethnicity_raw_outer | ALL | NULL | NULL | NULL | NULL | 84012 | |
| 2 | DEPENDENT SUBQUERY | school_data_race_ethnicity_raw_inner | ref | school_id,year,school_id_2 | year | 4 | rocdocs_main_drupal_7.school_data_race_ethnicity_raw_outer.year | 8402 | Using where |
+----+--------------------+--------------------------------------+------+----------------------------+------+---------+-----------------------------------------------------------------+-------+-------------+
2 rows in set (0.00 sec)
创建表格：
mysql> show create table school_data_race_ethnicity_raw;
+--------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+--------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| school_data_race_ethnicity_raw | CREATE TABLE `school_data_race_ethnicity_raw` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`school_id` varchar(255) NOT NULL,
`year` int(11) NOT NULL,
`race` varchar(255) NOT NULL,
`count` int(11) NOT NULL,
PRIMARY KEY (`id`),
KEY `school_id` (`school_id`,`year`),
KEY `year` (`year`,`race`),
KEY `school_id_2` (`school_id`)
) ENGINE=MyISAM AUTO_INCREMENT=84013 DEFAULT CHARSET=latin1 |
+--------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
mysql> show create table school_data_race_ethnicity_schools;
+------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| school_data_race_ethnicity_schools | CREATE TABLE `school_data_race_ethnicity_schools` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`school_id` varchar(255) NOT NULL,
`year` int(11) NOT NULL,
`race` varchar(255) NOT NULL,
`percent` decimal(15,2) NOT NULL,
PRIMARY KEY (`id`),
KEY `year` (`year`,`race`),
KEY `school_id` (`school_id`,`year`)
) ENGINE=MyISAM AUTO_INCREMENT=24961 DEFAULT CHARSET=latin1 |
+------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
mysql> show processlist;
+------+---------+--------------------+-----------------------+---------+------+--------------+------------------------------------------------------------------------------------------------------+
| Id | User | Host | db | Command | Time | State | Info |
+------+---------+--------------------+-----------------------+---------+------+--------------+------------------------------------------------------------------------------------------------------+
| 1739 | [REMOVED] | [REMOVED] | rocdocs_main_drupal_7 | Query | 1467 | Sending data | INSERT INTO school_data_race_ethnicity_schools (school_id, year, race, percent) (
SELECT school_id,y |
| 1800 | root | localhost | rocdocs_main_drupal_7 | Query | 0 | NULL | show processlist |
+------+---------+--------------------+-----------------------+---------+------+--------------+------------------------------------------------------------------------------------------------------+
2 rows in set (0.00 sec)
答案 0 :(得分：2)
由于您使用子查询计算百分比的方式，您的SELECT将会非常慢。它正在读取每一行的整年数据。如果您使用子查询来选择总计并加入到那个，那么它应该运行得更快。
在我的脑海中，这样的事情（虽然不理想）应该比现有的查询快得多：
select detail.school_id,
detail.year,
detail.race,
ROUND((detail.count / summary.total) * 100 ,2) as percent
FROM school_data_race_ethnicity_raw as detail
inner join (
select school_id, year, sum(count) as total
from school_data_race_ethnicity_raw
group by school_id, year
) as summary on summary.school_id = detail.school_id
and summary.year = detail.year
答案 1 :(得分：0)
让我们处理SELECT查询。让我们一块一块地做。对于每个不同的学校，种族和年份，您似乎想要一行。这很简单。
SELECT r.school_id, r.year, r.race, something
FROM school_data_race_ethnicity_raw r
GROUP BY r.school_id, r.year, r.race
现在让我们整理一下您的something指标。很难从你的问题中准确地说出来，但我猜。看起来你想要属于每个种族的学生比例。
因此我们需要处理两个摘要查询。一个按年给我们每所学校的学生总数。
SELECT r.school_id, r.year, SUM(count) count
FROM school_data_race_ethnicity_raw r
GROUP BY r.school_id, r.year
第二部分给出了按学校，年份和种族划分的学生总数。
SELECT r.school_id, r.year, r.race, SUM(count) count
FROM school_data_race_ethnicity_raw r
GROUP BY r.school_id, r.year, r.race
然后，我们需要将这两个查询连接在一起，就像它们是虚拟表一样，所以我们可以做分数：
SELECT t.school_id, t.year, u.race, u.count/t.count percent
FROM
(
SELECT r.school_id, r.year, SUM(count) count
FROM school_data_race_ethnicity_raw r
GROUP BY r.school_id, r.year
) t
LEFT JOIN
(
SELECT r.school_id, r.year, r.race, SUM(count) count
FROM school_data_race_ethnicity_raw r
GROUP BY r.school_id, r.year, r.race
) u ON (t.school_id = u.school_id AND t.year = u.year)
最后，你需要百分比，所以让我们将分数乘以100.0。
SELECT t.school_id, t.year, u.race, ROUND(100.0*u.count/t.count, 2) percent
FROM
(
SELECT r.school_id, r.year, SUM(count) count
FROM school_data_race_ethnicity_raw r
GROUP BY r.school_id, r.year
) t
LEFT JOIN
(
SELECT r.school_id, r.year, r.race, SUM(count) count
FROM school_data_race_ethnicity_raw r
GROUP BY r.school_id, r.year, r.race
) u ON (t.school_id = u.school_id AND t.year = u.year)