Break into multiple rows based on date range of a single row - tsql

Question

I have a table which captures appointments, some are single day appointments and some are multi day appointments, so the data looks like
AppointmentId StartDate EndDate
9 2017-04-12 2017-04-12
10 2017-05-01 2017-05-03
11 2017-06-01 2017-06-01
I want to split the multi day appointment as single days, so the result I am trying to achieve is like
AppointmentId StartDate EndDate
9 2017-04-12 2017-04-12
10 2017-05-01 2017-05-01
10 2017-05-02 2017-05-02
10 2017-05-03 2017-05-03
11 2017-06-01 2017-06-01
So I have split the appointment id 10 into multiple rows. I checked a few other questions like
here but those are to split just based on a single start date and end date and not based on table data

Answer 1

You can use a Calendar or dates table for this sort of thing.
For only 152kb in memory, you can have 30 years of dates in a table with this:
/* dates table */
declare #fromdate date = '20000101';
declare #years int = 30;
/* 30 years, 19 used data pages ~152kb in memory, ~264kb on disk */
;with n as (select n from (values(0),(1),(2),(3),(4),(5),(6),(7),(8),(9)) t(n))
select top (datediff(day, #fromdate,dateadd(year,#years,#fromdate)))
[Date]=convert(date,dateadd(day,row_number() over(order by (select 1))-1,#fromdate))
into dbo.Dates
from n as deka cross join n as hecto cross join n as kilo
cross join n as tenK cross join n as hundredK
order by [Date];
create unique clustered index ix_dbo_Dates_date
on dbo.Dates([Date]);
Without taking the actual step of creating a table, you can use it inside a common table expression with just this:
declare #fromdate date = '20161229';
declare #thrudate date = '20170103';
;with n as (select n from (values(0),(1),(2),(3),(4),(5),(6),(7),(8),(9)) t(n))
, dates as (
select top (datediff(day, #fromdate, #thrudate)+1)
[Date]=convert(date,dateadd(day,row_number() over(order by (select 1))-1,#fromdate))
from n as deka cross join n as hecto cross join n as kilo
cross join n as tenK cross join n as hundredK
order by [Date]
)
select [Date]
from dates;
Use either like so:
select
t.AppointmentId
, StartDate = d.date
, EndDate = d.date
from dates d
inner join appointments t
on d.date >= t.StartDate
and d.date <= t.EndDate
rextester demo: http://rextester.com/TNWQ64342
returns:
+---------------+------------+------------+
| AppointmentId | StartDate | EndDate |
+---------------+------------+------------+
| 9 | 2017-04-12 | 2017-04-12 |
| 10 | 2017-05-01 | 2017-05-01 |
| 10 | 2017-05-02 | 2017-05-02 |
| 10 | 2017-05-03 | 2017-05-03 |
| 11 | 2017-06-01 | 2017-06-01 |
+---------------+------------+------------+
Number and Calendar table reference:
Generate a set or sequence without loops - 1 - Aaron Bertrand
Generate a set or sequence without loops - 2 - Aaron Bertrand
Generate a set or sequence without loops - 3 - Aaron Bertrand
The "Numbers" or "Tally" Table: What it is and how it replaces a loop - Jeff Moden
Creating a Date Table/Dimension in sql Server 2008 - David Stein
Calendar Tables - Why You Need One - David Stein
Creating a date dimension or calendar table in sql Server - Aaron Bertrand
tsql Function to Determine Holidays in sql Server - Aaron Bertrand
F_table_date - Michael Valentine Jones

Answer 2

Clearly a Calendar/Tally table would be the way to go as SqlZim illustrated (+1), however you can use an ad-hoc tally table with a CROSS APPLY.
Example
Select A.AppointmentId
,StartDate = B.D
,EndDate = B.D
From YourTable A
Cross Apply (
Select Top (DateDiff(DD,A.StartDate,A.EndDate)+1) D=DateAdd(DD,-1+Row_Number() Over (Order By Number),A.StartDate)
From master..spt_values
) B
Returns
AppointmentId StartDate EndDate
9 2017-04-12 2017-04-12
10 2017-05-01 2017-05-01
10 2017-05-02 2017-05-02
10 2017-05-03 2017-05-03
11 2017-06-01 2017-06-01