基於等值列值查詢分段結果

Question

我想構建一個單一的查詢（或儘可能少）來分組數據集。所以給定了一些桶，我想返回基於特定列的結果。

所以給出一列叫做分數這是一個雙重包含：

90.00 
91.00 
94.00 
96.00 
98.00 
99.00 

我希望能夠使用GROUP BY子句中包含一個函數：

SELECT MIN（分），MAX（得分），SUM（得分）FROM表GROUP BY BUCKETS（得分，3）

理想情況下，這將返回3行（將結果分組到3個桶中，儘可能接近每個組的平均數） ）：

90.00, 91.00, 181.00 
94.00, 96.00, 190.00 
98.00, 99.00, 197.00 

是否有一些功能可以做到這一點？我想避免返回所有行並自己計算出存儲段。

戴夫

Answer 1

create table test (
id int not null auto_increment primary key, 
val decimal(4,2) 
) engine = myisam; 

insert into test (val) values 
(90.00), 
(91.00), 
(94.00), 
(96.00), 
(98.00), 
(99.00); 

select min(val) as lower,max(val) as higher,sum(val) as total from (
select id,val,@row:=@row+1 as row 
from test,(select @row:=0) as r order by id 
) as t 
group by ceil(row/2) 

+-------+--------+--------+ 
| lower | higher | total | 
+-------+--------+--------+ 
| 90.00 | 91.00 | 181.00 | 
| 94.00 | 96.00 | 190.00 | 
| 98.00 | 99.00 | 197.00 | 
+-------+--------+--------+ 
3 rows in set (0.00 sec) 

不幸MySQL沒有像ROWNUM解析函數（），所以你必須使用一些變量來效仿。一旦你這樣做了，你可以簡單地使用ceil（）函數來按照你喜歡的方式來分組每一行。希望儘管我的英語能夠幫助你。

set @r = (select count(*) from test); 
select min(val) as lower,max(val) as higher,sum(val) as total from (
select id,val,@row:=@row+1 as row 
from test,(select @row:=0) as r order by id 
) as t 
group by ceil(row/ceil(@r/3)) 

，或者使用單個查詢

select min(val) as lower,max(val) as higher,sum(val) as total from (
select id,val,@row:=@row+1 as row,tot 
from test,(select count(*) as tot from test) as t2,(select @row:=0) as r order by id 
) as t 
group by ceil(row/ceil(tot/3))