Mysql选择只有特定条件的结果

Question

这是我的问题：我有一个与不同国际项目相关的用户列表，我希望得到专门为美国项目工作的用户，所以让我们说如果有人为德国项目工作，我不想要他在名单中。 它涉及三个表：用户，项目，公司

这是第一个获取用于美国项目的用户的查询：

SELECT DISTINCT users.forename, users.surname, users.email, users.company_id,  users.user_id
FROM projects, company, users
WHERE projects.project_type = 'US'
AND company.project_id = projects.project_id
AND users.company_id = company.company_id
ORDER BY surname, forename

现在我如何排除还有其他国家项目的用户？

Answer 1

您可以使用NOT IN子句来排除在其他项目上工作的用户。

在条件添加到下面的行

WHERE projects.user_id 
  NOT IN (select user_id from projects where projects.project_type != 'US')

Answer 2

您可以加入表格并根据条件进行过滤

SELECT DISTINCT users.forename, users.surname, users.email, users.company_id,  users.user_id
FROM users
JOIN company USING (company_id)
JOIN projects USING (project_id)
WHERE projects.project_type = 'US'
ORDER BY surname, forename

此查询创建包含用户的行以及有关公司和项目的信息，并在使用条件WHERE projects.project_type = 'US'过滤这些行之后

Answer 3

你可以试试HAVING 。 如果用户仅在美国工作，则COUNT必须为1：

SELECT DISTINCT users.forename, COUNT(projects.*) AS c, users.surname, users.email, users.company_id,  users.user_id
FROM projects, company, users
WHERE projects.project_type = 'US'
AND company.project_id = projects.project_id
AND users.company_id = company.company_id
GROUP BY projects.project_type
HAVING c = 1
ORDER BY surname, forename

也许这段代码不起作用，无法检查，但你可以尝试这个方向。

Answer 4

not exists会做这个工作

SELECT DISTINCT users.forename, users.surname, users.email, users.company_id,  users.user_id
FROM projects, company, users
WHERE projects.project_type = 'US'
AND company.project_id = projects.project_id
AND users.company_id = company.company_id
AND NOT EXISTS (
    SELECT * 
      FROM projects notUS 
     WHERE notUS.project_type <> 'US' 
       AND notUS.user_id = users.user_id)
ORDER BY surname, forename

Answer 5

你可以用这个： -

SELECT DISTINCT users.forename, users.surname, users.email, users.company_id,  users.user_id
FROM projects, company, users
WHERE users.company_id = company.company_id
AND company.project_id = projects.project_id
AND projects.user_id 
IN (select user_id from projects where projects.project_type = 'US')
ORDER BY surname, forename

Answer 6

试试这个我觉得你需要MINUS：

SELECT 
    users.forename, users.surname, users.email, users.company_id,  users.user_id
FROM 
    users
where 
    user_id not in(SELECT DISTINCT user_id from users where company_id in
    (
        Select company_id from company where project_id = (
            Select project_id from projects where project_type != 'US'
        )
    ) 

Answer 7

你也可以这样做

SELECT DISTINCT
  users.forename,
  users.surname,
  users.email,
  users.company_id,
  users.user_id
FROM projects
  INNER JOIN company
    ON company.project_id = projects.project_id
  INNER JOIN users
    ON users.company_id = company.company_id
  INNER JOIN (SELECT *
          FROM projects
          WHERE project_type <> 'US') AS project
    ON project.project_id = projects.project_id
WHERE project.project_id IN NULL
GROUP BY projects.project_id
ORDER BY surname, forename