求教使用GROUP_CONCAT后字段的求和问题

commissioner 表如下：


arrangement 表如下：


现有sql语句如下：

 DROP TABLE IF EXISTS temp_arrangement;

     CREATE TABLE temp_arrangement  

     SELECT   

        `arrangement`.`id`,		

		`arrangement`.`projectid`,

        `arrangement`.`courseid`,

		`arrangement_date`.`date` AS `traindate`,

        GROUP_CONCAT(`arrangement`.`teacherid`  ORDER BY `arrangement`.`teacherid` ASC)  AS `teacherids`,

        `arrangement`.`commissionerids` AS `commissionerids`,

		GROUP_CONCAT(DISTINCT `commissioner`.`name`  ORDER BY `commissioner`.`id` ASC) AS `commissionernames`,

		`arrangement`.`time`,

		`arrangement`.`traindays`,

        SUM(CASE WHEN `arrangement`.`traindays`=0 THEN `arrangement`.`time` ELSE `arrangement`.`traindays` END) AS `usetime`

	FROM 

        `arrangement`

	INNER JOIN 

        `arrangement_date`

    ON 

        DATE(`arrangement_date`.`date`)  BETWEEN  DATE(`arrangement`.`startdate`) AND  DATE(`arrangement`.`enddate`)



	LEFT JOIN 

		`commissioner`

	ON FIND_IN_SET(`commissioner`.`id`,`arrangement`.`commissionerids`) 

  

	WHERE DATE( `arrangement_date`.`date`)  BETWEEN  DATE('2015-07-01')  AND  DATE('2015-07-10')



    GROUP BY  `arrangement`.`projectid`,`arrangement`.`courseid`, `arrangement_date`.`date` ;

    

	SELECT a.* FROM temp_arrangement AS a  ORDER BY 

    (SELECT MIN(b.traindate) FROM temp_arrangement AS b WHERE projectid=a.projectid),a.projectid,a.traindate;



 

执行结果如下图所示：


想实现GROUP_CONCAT('`arrangement`.`teacherid`')之后的teacherids不重复，且usetime应该以teacherids的个数为根据来进行求和，即：teacherids去重复后，如果teacherids为单个数字，没有逗号分隔，则usetime对应的应该是1，而不是上图中的2。
当然，GROUP_CONCAT(DISTINCT `arrangement`.`teacherid`）可以去重复，但usetime却不是想要 的效果。

想请教各位达人，要实现下图这种效果，要怎么改进sql语句呢？