问题描述
我有两张桌子一张员工和邮寄订阅员工看起来像这样:
I have two tables one Employee and mailing Subscriptions Employee looks like this:
姓名 (pk) |姓氏 |年龄
Name (pk) | Surname | Age
邮寄订阅
MailId (pk)|员工姓名 (fk)|描述 |日期
MailId (pk)| EmployeeName (fk)|Description | Date
我想为每个客户提供订阅号，因此我尝试了以下查询:
I wanted to subscription number for each customer, therefore I tried the following query:
Select COUNT(c.Name)
From Employee
INNER JOIN mailingSubscriptions as m ON c.Name = m.EmployeeName;
它将为我提供在邮件订阅中具有条目的每个员工的所有计数.
It will give me all counts for each Employee that has an entry in the mailing subscription.
我的问题是我想查看所有员工的计数，包括没有条目的员工(因此显示为 0)，我尝试了外部左/右连接，但它不起作用.难道我做错了什么?
My problem is that I want to see the counts for ALL the Employees, including the ones without an entry (therefore to show 0), I tried an outer left/right join, but it will not work. Am I doing something wrong?
推荐答案
SELECT c.name, count(m.mailid)
FROM Employee
LEFT JOIN mailingSubscriptions as m ON c.Name = m.EmployeeName
GROUP BY c.name;
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