1
count:通过分组,进行统计,与group by 联合使用,当count()得到的数作为查询条件,需要与having联合使用,而不是where
use datebase_name
go
create table text1
([number] [int] NOT NULL primary key,
[indate] [datetime] NULL,
[name] [nvarchar](255) NULL,
[grade] [nvarchar](255) NULL,
[teacher] [nvarchar](255) NULL,
[money] [money] NULL,
[class] [nvarchar](50) NULL,
[course] [nvarchar](50) NULL)
go
insert into text1
values(1,'2020-10-27','张三','98','刘四','4000','一年级','英语'),
(2,'2020-10-27','张三','98','刘四','4000','一年级','语文'),
(3,'2020-10-27','张三','98','刘四','4000','一年级','数学'),
(4,'2020-10-27','李四','98','刘四','4000','一年级','英语'),
(5,'2020-10-27','李四','98','刘四','4000','一年级','语文'),
(6,'2020-10-27','李四','98','刘四','4000','一年级','数学');
select count(name),course
from text1
where name = '张三'
group by course
having count(name) is not null
2
count:count可单独使用,统计的是符合条件的所有记录数量,count(0)与count(字段名1 /字段名2)作用相同
select count(0)
from text1