–聚合函數包括 例1:統計課程編号為CO1的最高分、最低分、平均分、學生數量
select MAX(grade) as ‘最高分’, MIN(grade) as ‘最低分’,
AVG(grade) as ’ 平均分’,COUNT(*) as ‘學生數量’,
from t_score
where cno =‘CO1’
例2:統計每一門課程的最高分、最低分、平均分、學生數量
select MAX(grade) as ‘最高分’, MIN(grade) as ‘最低分’,
AVG(grade) as ’ 平均分’,COUNT(*) as ‘學生數量’,
from t_score
GROUP BY cno
例3
聚合函數:
最大值max,最小值min,平均值avg,求和sum,總數count。
分組group by
分組條件:group by having…