优化SQL语句

刚开始学习SQL,下面的语句有没有更好的方法呀

SQL code:
DECLARE @Now datetime SET @Now = GETDATE() DECLARE @rqbc varchar(10) SET @rqbc = CONVERT(varchar(10), DATEADD(mi, - (SELECT StartDay from Parameter), @Now), 120)
SELECT CONVERT(varchar(19), @Now, 120) AS sj
, CONVERT(varchar(10), @Now, 120) AS rq
, @rqbc AS rqbc
, CASE WHEN CONVERT(varchar(8), @Now, 108) >= '08:30:00' AND CONVERT(varchar(8), @Now, 108) < '19:30:00' THEN '白班' ELSE '夜班' END AS bc
, CONVERT(varchar(10), DATEADD(mm, DATEDIFF(mm, 0, @rqbc), 0), 120) AS yf

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CASE WHEN CONVERT(varchar(8), @Now, 108) >= '08:30:00' AND CONVERT(varchar(8), @Now, 108) < '19:30:00' THEN '白班' ELSE '夜班' END AS bc

返回班次按照下列表中时间段返回如何做呀？
开始时间      结束时间    班次
07:30:00    16:30:00    一班
16:30:00    24:00:00    二班
24:00:00    07:30:00    三班

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我自己写的，还有好的方法吗？
SQL code:
DECLARE @Now datetime SET @Now = GETDATE() DECLARE @rqbc varchar(10) SET @rqbc = CONVERT(varchar(10), DATEADD(mi, - (SELECT StartDay from LSY_Parameter), @Now), 120)
SELECT CONVE