将两个日期时间戳与第一个日期和第二个时间组合在一起

我有一个表,在两个不同的列中存储约会的开始日期和结束日期。它们都是约会时间。这是为了便于导入旧数据。我不能改变结构。我正在使用Microsoft SQL Server。

ApptDate                   ApptTime
2012-02-16 00:00:00.000    1899-12-30 11:45:00.000
2012-02-16 00:00:00.000    1899-12-30 13:15:00.000
2012-02-16 00:00:00.000    1899-12-30 13:30:00.000

我需要做的是将这两个约会时间组合在一起。我正在调用存储过程。我的问题是,我最好的方式是什么?

ALTER PROCEDURE [dbo].[GetTodaysAppointsNonRepeating] 
    -- Add the parameters for the stored procedure here
    @DateToday DATETIME, @ClientID INT
AS
BEGIN
    -- SET NOCOUNT ON added to prevent extra result sets from
    -- interfering with SELECT statements.
    SET NOCOUNT ON;

    -- Insert statements for procedure here
    SELECT a.ID, a.ApptDate, a.ApptTime, a.ApptLength, a.checkedin, a.Entered, a.UserID, a.ProviderID, a.PatientID, CASE WHEN patient.FirstName is null then a.Name END as name, 
    CASE WHEN HomePhone !='' then HomePhone WHEN WorkPhone !='' THEN WorkPhone ELSE CellPhone END as Telephone
    FROM Appointments as a INNER JOIN Patient on a.PatientID = patient.id and 
    a.clientid = patient.clientid WHERE ApptDate = @DateToday and a.ClientID = @ClientID
    AND RepeatType = 'N'
END