如何仅从一个表 SQL SERVER 中比较日期

Question

我需要帮助，因为我正在做一个项目，我需要比较 SQL Server 中的日期，我需要获取在同一日期收到访问的人的姓名，但我做不到。

create table Visit (

    Id_Visit int not null identity primary key,
    NumberVisits int not null,
    DescriptionVisits varchar(500) not null,
    DateVisit date not null,
    TimeVisit time not null,
    Person int not null,
    foreign key(Person) references Person(NumPerson)
);

insert into Visit values(2, 'Visita pela filha Joana e pelo neto João', '05-18-2020', '15:30', 1);

insert into Visit values(1, 'Visita pelo amigo Artur', '08-10-2020', '10:00', 2);

insert into Visit values(1, 'Visita pelo filho Joaquim', '09-14-2020', '17:10', 3);

insert into Visit values(1, 'Visita pelo advogado Firminio', '08-11-2020', '15:50', 2);

insert into Visit values(3, 'Visita pelas amigas Belandina, Carmélia e Rosa', '08-10-2020', '14:30', 1);


--Change Date from visit 3

update Visit 
set DateVisit = cast('2020-05-18' as date)
where Id_Visit = 3

--Change Time from visit 3

update Visit
set TimeVisit = cast('15:30' as time)
where Id_Visit = 3

--Change Date from visit 2

update Visit
set DateVisit = cast('2020-05-18' as date)
where Id_Visit = 2;

我想做一个只显示在同一日期访问的人数的选择。

Answer 1

我认为这就是你想要的http://sqlfiddle.com/#!18/896ff/2/0

SELECT DISTINCT Person
FROM Visit
WHERE DateVisit IN (
  SELECT DateVisit
  FROM Visit
  GROUP By DateVisit
  HAVING COUNT(*) > 1
 )

这会在Visit表中找到不止一次存在的日期（即，当天有多次访问），然后提取访问过的Person 。

Answer 2

我想你的意思是这段代码

SELECT DateVisit ,COUNT(DISTINCT Person) AS PersonCount
FROM Visit GROUP BY DateVisit

您也可以使用条件

SELECT COUNT(DISTINCT Person) AS PersonCount
FROM Visit WHERE datevisit = '2020-05-18'