周总找我问个报表SQL实现逻辑的案例，废话不说给他看看。

原SQL：

SELECT d.tname   姓名,
       d.spname  岗位,
       d.sum_cnt 报单单量,
       d.min_cnt 放款单量,
       d.date    月份
FROM (SELECT *
      FROM (SELECT a.zts_name                                tname,
                   a.sp_name                                 spname,
                   CONVERT(ifnull(a.order_cnt, '0'), SIGNED) sum_cnt,
                   CONVERT(ifnull(b.order_cnt, '0'), SIGNED) min_cnt,
                   a.gmt_create DATE
            FROM
                (
                SELECT
                t.zts_name, t.sp_name, count( t.order_no ) AS order_cnt, DATE_FORMAT ( t.gmt_create, '%Y-%m' ) gmt_create
                FROM
                (
                SELECT
                zts.`name` AS zts_name,
    ztr.`name` AS sp_name,
    rto.order_no,
    rto.gmt_create AS gmt_create 
FROM
    AAAA rto
INNER JOIN BBBB rts ON rto.id = rts.order_id 
INNER JOIN CCCC zts ON rts.principal_id = zts.id 
INNER JOIN DDDD ztj ON zts.id = ztj.staff_id 
INNER JOIN EEEE ztr ON ztj.role_id = ztr.id 
WHERE
    rts.role = '7' 
    AND ztr.`description` = '客户经理'

    ) t 
   GROUP BY
    t.zts_name 
   ) A
   LEFT JOIN (
   SELECT
    t.zts_name,
    t.sp_name,
    count( t.order_no ) AS order_cnt,
    DATE_FORMAT( t.gmt_create, '%Y-%m' ) gmt_create 
   FROM
    (
SELECT
    zts.`name` AS zts_name,
    ztr.`name` AS sp_name,
    rto.order_no,
    rto.gmt_create AS gmt_create 
FROM
    AAAA rto
INNER JOIN BBBB rts ON rto.id = rts.order_id 
INNER JOIN CCCC zts ON rts.principal_id = zts.id 
INNER JOIN DDDD ztj ON zts.id = ztj.staff_id 
INNER JOIN EEEE ztr ON ztj.role_id = ztr.id 
WHERE
    rto.state IN ( 4010, 4030 ) 
    AND rts.role = '7' 
    AND ztr.`description` = '客户经理'

    ) t 
   GROUP BY
    t.zts_name 
   ) b
            ON A.zts_name = b.zts_name
                AND A.gmt_create = b.gmt_create) c
      ORDER BY c.date ASC,
               CONVERT(c.sum_cnt, signed) DESC) d;

精简后的结果集：

周总的意思很简单，就是以 月份 来分组，求出 报单数量 在不同月份中的中位数就行。

这道题读者不需要过多关注原来的SQL是如何写的，只需要把重点放在如何取 报单数量 的中位数即可。

中位数：在一个数列中，如果按照大小顺序排列，中位数就是位于中间的那个数。

这道SQL的解题思路其实很简单：

1、使用 DENSE_RANK 开窗函数对 月份分组 ，然后对 报单数量排序，注意：不能使用 ROW_NUMBER() 和 RANK() 进行排序，这两个函数一个会给连续的序号，另外一个会跳号。

2、然后对 DENSE_RANK 开窗函数 的排序结果进行 max 开窗取每个月的最大序号。

3、最后使用 每个月的最大序号除以2 就可以得出不同月份的中位数。

最终SQL代码：

SELECT *
FROM (

         /*      FLOOR(j.最大的编号 / 2) 中位数编号

                最后使用 每个月的最大序号除以2 就可以得出不同月份的中位数。

         */

      SELECT j.姓名,
             j.岗位,
             j.报单单量,
             j.放款单量,
             j.月份,
             j.编号,
             FLOOR(j.最大的编号 / 2) 中位数编号
      FROM (
      
                  /*  MAX(x.rn) OVER (PARTITION BY x.月份 ) 最大的编号

                        然后对 DENSE_RANK 开窗函数 的排序结果进行 max 开窗取每个月的最大序号

                  */
      
            SELECT x.姓名,
                   x.岗位,
                   x.报单单量,
                   x.放款单量,
                   x.月份,
                   x.rn                                  编号,
                   MAX(x.rn) OVER (PARTITION BY x.月份 ) 最大的编号
            FROM (
            
                  /*  DENSE_RANK() OVER (PARTITION BY d.date ORDER BY d.sum_cnt) rn    

                        对月份分组 ，然后对报单数量排序

                  */
            
                    SELECT  
                         d.tname                                                    姓名,
                         d.spname                                                   岗位,
                         d.sum_cnt                                                  报单单量,
                         d.min_cnt                                                  放款单量,
                         d.date                                                     月份,
                         DENSE_RANK() OVER (PARTITION BY d.date ORDER BY d.sum_cnt) rn
                  FROM (
                  
                  /*  以下SQL为原始SQL */
                  SELECT *
                        FROM (
                        SELECT a.zts_name                                tname,
                                     a.sp_name                                 spname,
                                     CONVERT(ifnull(a.order_cnt, '0'), SIGNED) sum_cnt,
                                     CONVERT(ifnull(b.order_cnt, '0'), SIGNED) min_cnt,
                                     a.gmt_create DATE
                              FROM
                                  (
                                  SELECT
                                  t.zts_name, t.sp_name, count( t.order_no ) AS order_cnt, DATE_FORMAT ( t.gmt_create, '%Y-%m' ) gmt_create
                                  FROM
                                  (
                                  SELECT
                                  zts.`name` AS zts_name,
    ztr.`name` AS sp_name,
    rto.order_no,
    rto.gmt_create AS gmt_create
FROM
    AAAA rto
INNER JOIN BBBB rts ON rto.id = rts.order_id
INNER JOIN CCCC zts ON rts.principal_id = zts.id
INNER JOIN DDDD ztj ON zts.id = ztj.staff_id
INNER JOIN EEEE ztr ON ztj.role_id = ztr.id
WHERE
    rts.role = '7'
    AND ztr.`description` = '客户经理'

    ) t
   GROUP BY
    t.zts_name
   ) A
   LEFT JOIN (
   SELECT
    t.zts_name,
    t.sp_name,
    count( t.order_no ) AS order_cnt,
    DATE_FORMAT( t.gmt_create, '%Y-%m' ) gmt_create
   FROM
    (
SELECT
    zts.`name` AS zts_name,
    ztr.`name` AS sp_name,
    rto.order_no,
    rto.gmt_create AS gmt_create
FROM
    AAAA rto
INNER JOIN BBBB rts ON rto.id = rts.order_id
INNER JOIN CCCC zts ON rts.principal_id = zts.id
INNER JOIN DDDD ztj ON zts.id = ztj.staff_id
INNER JOIN EEEE ztr ON ztj.role_id = ztr.id
WHERE
    rto.state IN ( 4010, 4030 )
    AND rts.role = '7'
    AND ztr.`description` = '客户经理'

    ) t
   GROUP BY
    t.zts_name
   ) b
                              ON A.zts_name = b.zts_name
                                  AND A.gmt_create = b.gmt_create) c
                        ORDER BY c.date ASC,
                                 CONVERT(c.sum_cnt, signed) DESC) d) x) j) g
WHERE g.编号 = g.中位数编号;

最后可以看到该SQL已经改写成功，可以列出不同月份 达到中位数的销售姓名的单量。