SQL Query用于替换另一个表的记录

Question

以下代码会产生错误：

select lastname, firstname, workphone, homephone 
from members if (workphone is null) then workphone = homephone;

我正在尝试从名为lastnames的表中选择firstnames，members和您的电话号码。如果成员“workphone is null我需要将其替换为homephone。

如果需要，我会非常乐意澄清。

Answer 1

select lastname, firstname, 
case when (workphone is null) then homephone  else workphone end as workphone 
, homephone 
from members;

Answer 2

您可以使用COALESCE函数，该函数返回给定的第一个非null参数：

SELECT lastname, firstname, homephone, COALESCE(workphone, homephone) AS workphone
FROM   members