mysql COALESCE用法 ，GROUP_CONCAT分组用法

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sdroot.dept_name company,         COALESCE(         (case when sd5.dept_name = sdroot.dept_name then null else sd5.dept_name end) ,         (case when sd4.dept_name in(sdroot.dept_name,sd5.dept_name)  then null else sd4.dept_name end) ,         (case when sd3.dept_name in(sdroot.dept_name,sd4.dept_name) then null else sd3.dept_name end) ,         (case when sd2.dept_name in(sdroot.dept_name,sd3.dept_name,sd4.dept_name)  then null else sd2.dept_name end) ,         (case when sd1.dept_name in(sdroot.dept_name,sd3.dept_name,sd2.dept_name,sd3.dept_name,sd4.dept_name) then null else sd1.dept_name end)) deptName0,         COALESCE(         (case when sd1.order_num = '3' and sd1.dept_name is not Null then sd1.dept_name  end) ,         (case when sd2.order_num = '3' and sd2.dept_name is not Null then sd2.dept_name  end) ,         (case when sd3.order_num = '3' and sd3.dept_name is not Null then sd3.dept_name  end) ,         (case when sd4.order_num = '3'and sd4.dept_name is not Null then sd4.dept_name  end)         ) deptName1,           coalesce(         (case when sd1.order_num = '4' and sd1.dept_name is not Null then sd1.dept_name end) ,         (case when sd2.order_num = '4' and sd2.dept_name is not Null then sd2.dept_name  end) ,         (case when sd3.order_num = '4' and sd3.dept_name is not Null then sd3.dept_name end) ,         (case when sd4.order_num = '4' and sd4.dept_name is not Null then sd4.dept_name  end)         ) deptName2,           coalesce(         (case when sd1.order_num = '5' and sd1.dept_name is not Null then sd1.dept_name end) ,         (case when sd2.order_num = '5' and sd2.dept_name is not Null then sd2.dept_name  end) ,         (case when sd3.order_num = '5' and sd3.dept_name is not Null then sd3.dept_name end) ,         (case when sd4.order_num = '5' and sd4.dept_name is not Null then sd4.dept_name  end) ,         (case when sd5.order_num = '5' and sd5.dept_name is not Null then sd5.dept_name  end)         ) deptName3,         sd.dept_name deptName,         (select GROUP_CONCAT(c.dept_name ORDER BY c.dept_id asc) as deptNameAll  from sys_dept c where find_in_set (c.dept_id ,sd.ancestors)) as deptNameAll,