PostgreSQL

Question

我有表：

company_employees:

id_employee
id_company

员工：

id_employee
name

公司：

id_company
name

如果我执行这样的查询：

SELECT companies.name AS Company, employees.name AS Employee FROM employees
INNER JOIN company_employees ON company_employees.id_employee = employees.id_employee
INNER JOIN companies ON companies.id_company = company_employees.id_company

显示：

+-----------+--------------+
|  Company  |   Employee   |
+-----------+--------------+
| Microsoft | John Smith   |
| Microsoft | Mike Brown   |
| IBM       | Chris Miller |
+-----------+--------------+

我只想显示公司名称 (companies.name)，其中员工 'John Smith' 和 'Mike Brown'。所以查询应该显示：

+-----------+
|   name    |
+-----------+
| Microsoft |
+-----------+

你知道怎么做吗？谢谢！

Answer 1

我们可以尝试按公司名称聚合，然后断言：

每个公司组中仅有的两个名字是'John Smith'和'Mike Brown'
每个公司组中不同名称的数量是两个

这两个条件都意味着结果集中的任何公司都符合您的条件。

SELECT
    c.name AS Company
FROM employees e
INNER JOIN company_employees ce
    ON ce.id_employee = ee.id_employee
INNER JOIN companies c
    ON c.id_company = ce.id_company
WHERE
    e.name IN ('John Smith', 'Mike Brown')
GROUP BY
    c.name
HAVING
    MIN(e.name) <> MAX(e.name);

Answer 2

如果 2 个不同的员工在下面的同一家公司工作，您可以像下面这样尝试

SELECT
    c.name AS Company
FROM employees e
INNER JOIN company_employees ce
    ON ce.id_employee = e.id_employee
INNER JOIN companies c
    ON c.id_company = ce.id_company

GROUP BY
    c.name
    HAVING
    count(distinct e.name)=2

DEMO in fiddle

company
Microsoft

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PostgreSQL - WHERE condition which refers to 2 different records and should be TRUE

sql

relational-division