SQL query to convert date ranges to per day records

Question

Requirements

1. I have data table that saves data in date ranges.
2. Each record is allowed to overlap previous record(s) (record has a CreatedOn da

Answer 1

Actually, since you are working with dates, a Calendar table would be more helpful.

Declare @StartDate date
Declare @EndDate date

;With Calendar As
    (
    Select @StartDate As [Date]
    Union All
    Select DateAdd(d,1,[Date])
    From Calendar
    Where [Date] < @EndDate
    )
Select ...
From Calendar
    Left Join MyTable
        On Calendar.[Date] Between MyTable.Start And MyTable.End
Option ( Maxrecursion 0 );

Addition

Missed the part about the trumping rule in your original post:

Set DateFormat MDY;
Declare @StartDate date = '20110101';
Declare @EndDate date = '20110501';

-- This first CTE is obviously to represent
-- the source table
With SampleData As 
    (
    Select 1 As Id
        , Cast('20110101' As date) As RangeFrom
        , Cast('20110331' As date) As RangeTo
        , Cast('07:00' As time) As Starts
        , Cast('15:00' As time) As Ends
        , CURRENT_TIMESTAMP As CreatedOn
    Union All Select 2, '20110401', '20110531', '08:00', '16:00', DateAdd(s,1,CURRENT_TIMESTAMP )
    Union All Select 3, '20110301', '20110430', '06:00', '14:00', DateAdd(s,2,CURRENT_TIMESTAMP )
    )
    , Calendar As
    (
    Select @StartDate As [Date]
    Union All
    Select DateAdd(d,1,[Date])
    From Calendar
    Where [Date] < @EndDate
    )
    , RankedData As
    (
    Select C.[Date]
        , S.Id
        , S.RangeFrom, S.RangeTo, S.Starts, S.Ends
        , Row_Number() Over( Partition By C.[Date] Order By S.CreatedOn Desc ) As Num
    From Calendar As C
        Join SampleData As S
            On C.[Date] Between S.RangeFrom And S.RangeTo
    )
Select [Date], Id, RangeFrom, RangeTo, Starts, Ends
From RankedData
Where Num = 1   
Option ( Maxrecursion 0 );

In short, I rank all the sample data preferring the newer rows that overlap the same date.

Answer 2

Why do it all in DB when you can do it better in memory

This is the solution (I eventually used) that seemed most reasonable in terms of data transferred, speed and resources.

1. get actual range definitions from DB to mid tier (smaller amount of data)
2. generate in memory calendar of a certain date range (faster than in DB)
3. put those DB definitions in (much easier and faster than DB)

And that's it. I realised that complicating certain things in DB is not not worth it when you have executable in memory code that can do the same manipulation faster and more efficient.