如何从这个表中选择并添加平均值然后排序

Question

  

可能重复：
  how to select, average and sort in mysql table

我在mySql中有一张表，如图所示

我想写一个查询，结果将按LESSON列分组，并添加新行，即LESSON列的平均值和总和CNT列值....

我使用这个查询但它给出的结果如图3所示，在这种情况下我不能按PERC排序

select no, STUD_ID,CLASS,LESSON, AVG(PERC) as PERC,SUM(CNT) as CNT from t_lesson where LESSON='CHEM' group by CLASS
union all
select no,STUD_ID,CLASS,'AVERAGE' as LESSON, AVG(PERC) as PERC, SUM(CNT) as CNT from t_lesson where LESSON='CHEM' group by LESSON

Answer 1

select * from <your query> order by PERC

wich：

select * from (

select no, STUD_ID,CLASS,LESSON, AVG(PERC) as PERC,SUM(CNT) as CNT from t_lesson where LESSON='CHEM' group by CLASS
union all
select no,STUD_ID,CLASS,'AVERAGE' as LESSON, AVG(PERC) as PERC, SUM(CNT) as CNT from t_lesson where LESSON='CHEM' group by LESSON

) as sub order by PERC DESC