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  • count 用法

    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

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  • 原文地址:https://www.cnblogs.com/sjqw1ws/p/13883192.html
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