sql-server-2008 - SQL Server - 根据条件构造更新 where 子句

Question

请参阅以下查询：

Update Employee
Set AccountManagerId = a.AM_ID
FROM Employee e INNER JOIN AccountManager a on e.Id = a.Id
WHERE

**努力构造下面的部分（需要添加到where子句中）**

If a.Department is not null then [FOLLOWING NEEDS TO BE ADDED TO WHERE CLAUSE] (e.Department = a.department)

努力将其添加到 where 子句。因此，如果部门不为 NULL，则将其添加到 WHERE 子句

Answer 1

你不能这样做：

Update Employee
Set AccountManagerId = a.AM_ID,
e.Department = a.department
FROM Employee e INNER JOIN AccountManager a on e.Id = a.Id
WHERE
a.Department IS NOT NULL

Answer 2

为什么不向联接添加另一个条件？

我相信这将实现您的意图，仅更新员工与具有部门的匹配客户经理。

UPDATE Employee
SET AccountManagerId = a.AM_ID
FROM Employee e 
INNER JOIN AccountManager a 
ON e.Id = a.Id
AND
e.Department = a.Department

Answer 3

Update Employee
Set AccountManagerId = a.AM_ID
FROM Employee e INNER JOIN AccountManager a on e.Id = a.Id
WHERE ((a.Department IS NULL) || (e.Department = a.department))