我通常做的事情是这样的

What I typically do is something like

WHERE ( @UserID IS NULL OR UserID = @UserID )

为什么它没有被索引?索引 FK 通常是一种很好的形式，因为您经常加入它们......

And why isn't it indexed? It's generally good form to index FKs, since you often join on them...

如果您担心查询计划存储，只需执行以下操作:创建过程...重新编译

If you're worried about query plan storage, simply do: CREATE PROCEDURE ... WITH RECOMPILE