mysql - 如何从此表中选择并添加平均值然后排序

Question

可能重复：
如何在 mysql 表中选择、平均和排序

我在 mySql 中有一个表，就像这张图片一样

我想编写一个查询，其结果将按 LESSON 列分组，并添加新行，即 LESSON 列的平均值和 CNT 列值的总和....

我使用这个查询，但它给出的结果如图 3 所示，在这种情况下我无法按 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

至：

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