SELECT readDate as Interval, tagname ,round(value,3) as value, amendedValue
FROM [GasNominations].[dbo].[GasData]
WHERE readDate between 
             dateadd(hour, 7, DATEADD(day, DATEDIFF(day, 0, GETDATE()), -1))   
             and dateadd(hour, 6, DATEADD(day, DATEDIFF(day, 0, GETDATE()), 0))
order by tagname, readdate

declare @from_date datetime, @to_date datetime

select @from_date ='20121101', @to_date='20121102'
SELECT readDate as Interval, tagname ,round(value,3) as value, amendedValue
FROM [GasNominations].[dbo].[GasData]
WHERE readDate between 
             dateadd(hour, 7, DATEADD(day, DATEDIFF(day, 0, @from_date , -1))   
             and dateadd(hour, 6, DATEADD(day, DATEDIFF(day, 0, @to_date ), 0))
order by tagname, readdate