美好的一天,
我使用以下代码计算9天移动平均值。
SELECT SUM(close)
FROM tbl
WHERE date <= '2002-07-05'
AND name_id = 2
ORDER BY date DESC
LIMIT 9
但它不起作用,因为它在调用限制之前首先计算所有返回的字段。换句话说,它将计算在该日期之前或之前的所有关闭,而不仅仅是最后的9。
所以我需要从返回的select中计算SUM,而不是直接计算它。
IE。从SELECT ...
中选择SUM现在我将如何做到这一点并且成本非常高还是有更好的方法?
答案 0 :(得分:10)
如果你想要每个日期的移动平均线,那么试试这个:
SELECT date, SUM(close),
(select avg(close) from tbl t2 where t2.name_id = t.name_id and datediff(t2.date, t.date) <= 9
) as mvgAvg
FROM tbl t
WHERE date <= '2002-07-05' and
name_id = 2
GROUP BY date
ORDER BY date DESC
它使用相关子查询来计算9个值的平均值。
答案 1 :(得分:5)
使用类似
的内容SELECT
sum(close) as sum,
avg(close) as average
FROM (
SELECT
(close)
FROM
tbl
WHERE
date <= '2002-07-05'
AND name_id = 2
ORDER BY
date DESC
LIMIT 9 ) temp
内部查询以desc
顺序返回所有已过滤的行,然后您avg
,sum
向上返回这些行。
您提供的query
不起作用的原因是由于首先计算sum
并在{{1}之后应用LIMIT
子句}已经计算过,给出了所有存在行的sum
答案 2 :(得分:5)
从MySQL 8开始,您应该为此使用窗口函数。使用窗口RANGE
子句,您可以在一定间隔内创建一个logical window,这非常强大。像这样:
SELECT
date,
close,
AVG (close) OVER (ORDER BY date DESC RANGE INTERVAL 9 DAY PRECEDING)
FROM tbl
WHERE date <= DATE '2002-07-05'
AND name_id = 2
ORDER BY date DESC
例如:
WITH t (date, `close`) AS (
SELECT DATE '2020-01-01', 50 UNION ALL
SELECT DATE '2020-01-03', 54 UNION ALL
SELECT DATE '2020-01-05', 51 UNION ALL
SELECT DATE '2020-01-12', 49 UNION ALL
SELECT DATE '2020-01-13', 59 UNION ALL
SELECT DATE '2020-01-15', 30 UNION ALL
SELECT DATE '2020-01-17', 35 UNION ALL
SELECT DATE '2020-01-18', 39 UNION ALL
SELECT DATE '2020-01-19', 47 UNION ALL
SELECT DATE '2020-01-26', 50
)
SELECT
date,
`close`,
COUNT(*) OVER w AS c,
SUM(`close`) OVER w AS s,
AVG(`close`) OVER w AS a
FROM t
WINDOW w AS (ORDER BY date DESC RANGE INTERVAL 9 DAY PRECEDING)
ORDER BY date DESC
通往:
date |close|c|s |a |
----------|-----|-|---|-------|
2020-01-26| 50|1| 50|50.0000|
2020-01-19| 47|2| 97|48.5000|
2020-01-18| 39|3|136|45.3333|
2020-01-17| 35|4|171|42.7500|
2020-01-15| 30|4|151|37.7500|
2020-01-13| 59|5|210|42.0000|
2020-01-12| 49|6|259|43.1667|
2020-01-05| 51|3|159|53.0000|
2020-01-03| 54|3|154|51.3333|
2020-01-01| 50|3|155|51.6667|
答案 3 :(得分:0)
此查询很快:
select date, name_id,
case @i when name_id then @i:=name_id else (@i:=name_id)
and (@n:=0)
and (@a0:=0) and (@a1:=0) and (@a2:=0) and (@a3:=0) and (@a4:=0) and (@a5:=0) and (@a6:=0) and (@a7:=0) and (@a8:=0)
end as a,
case @n when 9 then @n:=9 else @n:=@n+1 end as n,
@a0:=@a1,@a1:=@a2,@a2:=@a3,@a3:=@a4,@a4:=@a5,@a5:=@a6,@a6:=@a7,@a7:=@a8,@a8:=close,
(@a0+@a1+@a2+@a3+@a4+@a5+@a6+@a7+@a8)/@n as av
from tbl,
(select @i:=0, @n:=0,
@a0:=0, @a1:=0, @a2:=0, @a3:=0, @a4:=0, @a5:=0, @a6:=0, @a7:=0, @a8:=0) a
where name_id=2
order by name_id, date
如果你需要平均超过50或100的值,那么编写是很乏味的,但是 值得努力。速度接近有序选择。
答案 4 :(得分:0)
另一种技术是做表:
CREATE TABLE `tinyint_asc` (
`value` tinyint(3) unsigned NOT NULL default '0',
PRIMARY KEY (value)
) ;
INSERT INTO `tinyint_asc` VALUES (0),(1),(2),(3),(4),(5),(6),(7),(8),(9),(10),(11),(12),(13),(14),(15),(16),(17),(18),(19),(20),(21),(22),(23),(24),(25),(26),(27),(28),(29),(30),(31),(32),(33),(34),(35),(36),(37),(38),(39),(40),(41),(42),(43),(44),(45),(46),(47),(48),(49),(50),(51),(52),(53),(54),(55),(56),(57),(58),(59),(60),(61),(62),(63),(64),(65),(66),(67),(68),(69),(70),(71),(72),(73),(74),(75),(76),(77),(78),(79),(80),(81),(82),(83),(84),(85),(86),(87),(88),(89),(90),(91),(92),(93),(94),(95),(96),(97),(98),(99),(100),(101),(102),(103),(104),(105),(106),(107),(108),(109),(110),(111),(112),(113),(114),(115),(116),(117),(118),(119),(120),(121),(122),(123),(124),(125),(126),(127),(128),(129),(130),(131),(132),(133),(134),(135),(136),(137),(138),(139),(140),(141),(142),(143),(144),(145),(146),(147),(148),(149),(150),(151),(152),(153),(154),(155),(156),(157),(158),(159),(160),(161),(162),(163),(164),(165),(166),(167),(168),(169),(170),(171),(172),(173),(174),(175),(176),(177),(178),(179),(180),(181),(182),(183),(184),(185),(186),(187),(188),(189),(190),(191),(192),(193),(194),(195),(196),(197),(198),(199),(200),(201),(202),(203),(204),(205),(206),(207),(208),(209),(210),(211),(212),(213),(214),(215),(216),(217),(218),(219),(220),(221),(222),(223),(224),(225),(226),(227),(228),(229),(230),(231),(232),(233),(234),(235),(236),(237),(238),(239),(240),(241),(242),(243),(244),(245),(246),(247),(248),(249),(250),(251),(252),(253),(254),(255);
你可以这样使用它之后:
select date_add(tbl.date, interval tinyint_asc.value day) as mydate, count(*), sum(myvalue)
from tbl inner join tinyint_asc.value <= 30 -- for a 30 day moving average
where date(date_add(o.created_at, interval tinyint_asc.value day)) between '2016-01-01' and current_date()
group by mydate