WHERE 与 HAVING 区别

create table class_score
(

class_name nvarchar(10),

stu_name nvarchar(10),

score int

);

insert into class_score
values
(N'一班',N'小明',85),
(N'一班',N'小红',55),
(N'一班',N'小刚',90),
(N'二班',N'小丽',78),
(N'二班',N'小亮',60),
(N'三班',N'小华',45);

select
class_name as 班级,
count(*) as 及格人数
from class_score
where score >=60
group by class_name;

select
class_name as 班级,
count() as 及格人数
from class_score
where score >=60
group by class_name
having count() >=2;

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WHERE 管人（原始数据），HAVING 管组（统计结果）
行过滤用 WHERE，组过滤用 HAVING
聚合条件写 HAVING，普通条件写 WHERE