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CREATE TABLE `student_t` (
`id` varchar(32) NOT NULL,
`value` int(11) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
insert into student_t (id,`value`)
values ('A',40),
('B',50),
('C',60),
('D',70),
('E',80),
('F',90);
- 第一步先给表加一个列,列里面是对分数的排序(即标明了位置)
SELECT
id,
@INDEX := @INDEX + 1 AS myindex,
`VALUE` -- myindex代表的是这一列数,@index是位置
FROM
student_t
INNER JOIN ( SELECT @INDEX := 0 ) AS initvar ON 1 = 1
ORDER BY
`VALUE` #最内层
- 当记录是奇数时,中位数中间位置的数;当记录是偶数时,中位数是中间两个数的平均
SELECT
GROUP_CONCAT( id ),
avg( `VALUE` )
FROM
(#第二层开始
SELECT
id,
@INDEX := @INDEX + 1 AS myindex,
`VALUE` -- myindex代表的是这一列数,@index是位置
FROM
student_t
INNER JOIN ( SELECT @INDEX := 0 ) AS initvar ON 1 = 1
ORDER BY
`VALUE` #最内层
) AS t
WHERE
myindex = floor( @INDEX / 2+1 ) OR myindex = ceil( @INDEX / 2 )
- 四分位数
SELECT
GROUP_CONCAT( id ),
avg( `VALUE` )
FROM
(#第二层开始
SELECT
id,
@INDEX := @INDEX + 1 AS myindex,
`VALUE` -- myindex代表的是这一列数,@index是位置
FROM
student_t
INNER JOIN ( SELECT @INDEX := 0 ) AS initvar ON 1 = 1
ORDER BY
`VALUE` #最内层
) AS t
WHERE
myindex = floor(( @INDEX+1) /4 )
SELECT
GROUP_CONCAT( id ),
avg( `VALUE` )
FROM
(#第二层开始
SELECT
id,
@INDEX := @INDEX + 1 AS myindex,
`VALUE` -- myindex代表的是这一列数,@index是位置
FROM
student_t
INNER JOIN ( SELECT @INDEX := 0 ) AS initvar ON 1 = 1
ORDER BY
`VALUE` #最内层
) AS t
WHERE
myindex = floor(3*( @INDEX+1) /4 )