小编给大家分享一下MySQL百分位数计算如何进行优化,相信大部分人都还不怎么了解,因此分享这篇文章给大家参考一下,希望大家阅读完这篇文章后大有收获,下面让我们一起去了解一下吧!

主要是采用存储过程,在中间计算结果中,增加了一个索引

原来的SQL

select t5.query_time,t5.ts,t2.v from (

select query_time,total,v, floor(1+(total-1)*v) rn

from (

select query_time,count(*) total from t group by query_time

) t3, (select 0.71 v,1 seq union all select 0.81,2 union all select 0.91,3) t4

)

t2 inner join (

select

query_time,

case when @gid=query_time then @rn:=@rn+1 when @gid:=query_time then @rn:=1 end rn,

ts

from (

select * from t ,(select @gid:='',@rn:=0) vars order by query_time,ts

) t1

) t5 on (t2.query_time=t5.query_time and t2.rn=t5.rn )



改进为存储过程

drop procedure p;

delimiter $$

create procedure p()

begin

drop table if exists tmp_result;


create temporary table tmp_result(

query_time date,

rn int,

ts float,

key(query_time,rn)

) engine =memory;


insert ignore into tmp_result

select

query_time ,

case when @gid=query_time then @rn:=@rn+1 when @gid:=query_time then @rn:=1 end rn,

ts

from (

select * from t ,(select @gid:='',@rn:=0) vars order by query_time,ts

) t1 ;


select t5.query_time,t5.ts,t2.v from (

select query_time,total,v, floor(1+(total-1)*v) rn

from (

select query_time,count(*) total from t group by query_time

) t3, (select 0.71 v,1 seq union all select 0.81,2 union all select 0.91,3) t4

)

t2 inner join tmp_result t5 on (t2.query_time=t5.query_time and t2.rn=t5.rn );

end $$


delimiter ;


call p

使用存储过程 一般 11秒 左右

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