Question

我目前有2个表，我正在使用INNER JOIN子句进行查询。我的第一个标记为departments的表非常简单，只包含3个字段--deptID，deptName和companyID。我的第二个标记为departmentMemberships的表更简单，只包含2个字段--deptID和employeeID。我当前的SQL语句查询这两个表并返回所有deptID，deptName和每个部门的员工数。如果上述部门中没有任何员工，我的查询将不会返回部门。这是我目前的查询。

`SELECT departments.deptID, departments.deptName,
COUNT(departmentMemberships.deptID) AS employeeCount
FROM departmentMemberships
INNER JOIN departments
ON departmentMemberships.deptID = departments.deptID
WHERE departments.companyID = 1
GROUP BY departments.deptID, departments.deptName
ORDER BY departments.deptName ASC;`

请原谅我对TSQL的经验不足，但我怎么能改变这个查询以返回所有部门，包括那些没有员工注册的部门？

非常感谢

Answer 1

如上所述，请将INNER JOIN更改为RIGHT OUTER JOIN。但我更喜欢自己LEFT JOIN;它更容易遵循。即：

SELECT departments.deptID
     , departments.deptName
     , COUNT(departmentMemberships.deptID) AS employeeCount
FROM departments
LEFT OUTER JOIN departmentMemberships
ON departmentMemberships.deptID = departments.deptID
WHERE departments.companyID = 1
GROUP BY departments.deptID, departments.deptName
ORDER BY departments.deptName ASC

SQL内部联接，其中记录不存在

1 个答案: