sql - SQL - 使用 Count 时为 0

Question

我有一个人的名单，他们的职业如下：

Doctor Male
Teacher  Male
Principal Male
Nurse Female
Doctor Male

当我按专业对它们进行分组时，我希望 Access 为不在我拥有的子列表中的任何专业返回 0。这是我正在使用的代码：

SELECT Profession.Profession, Count(Profession.Profession) AS CountOfProfession
FROM People INNER JOIN Profession ON People.PeopleID = Profession.PeopleID
WHERE (((People.Sex)="Male"))
GROUP BY Profession.Profession;

我希望它为医生产生 2，因为有 2 名男性，但也为护士产生 0，因为没有男性护士。请让我知道我该怎么做，谢谢！

Answer 1

你需要一个外部连接。我切换了表格的顺序，所以它是left join：

SELECT Profession.Profession,
       sum(iif(people.sex = "Male", 1, 0)) AS CountOfProfession
FROM Profession LEFT JOIN
     ON People.PeopleID = Profession.PeopleID 
GROUP BY Profession.Profession;

Answer 2

这可以通过外部连接并将条件从子句移动WHERE到ON子句来完成：

SELECT Profession.Profession, 
       COUNT(People.PeopleID) AS CountOfProfession
FROM Profession 
  LEFT JOIN People 
    ON (  People.PeopleID = Profession.PeopleID
      AND People.Sex = 'Male' )
GROUP BY Profession.Profession ;