如何在创建视图时筛选Comments.FK_CommentID非空的记录

只需在关联表的语句之后、排序语句之前，添加过滤FK_CommentID非空的条件即可。修改后的完整SQL代码如下：

CREATE VIEW Comments_of_comments AS 
SELECT User.Username AS User, Comments.content AS Comment, Comments.FK_CommentID AS 'Commented on' 
FROM Comments 
INNER JOIN User ON Comments.UserID = User.UserID 
WHERE Comments.FK_CommentID IS NOT NULL
ORDER BY User ASC;

添加WHERE Comments.FK_CommentID IS NOT NULL后，视图就只会返回FK_CommentID字段不为空的记录了。

内容的提问来源于stack exchange，提问作者rainer