SQL Server中的IF EXISTS（SELECT）无法按预期工作

I have a code like this:

我有这样的代码：

IF EXISTS (SELECT * FROM table WHERE id = @id)
BEGIN
    UPDATE table
    SET stock = stock + @stock
    WHERE id = @id
END
ELSE
BEGIN
    INSERT INTO [table] ([id], [name], [stock])
    VALUES (@id, @name, @stock)
END
IF EXISTS