Next Appointment Algorithm

• Question

• User1122355199 posted

Hello everyone and thanks for your help in advance.  I'm not sure if this is the correct forum, but I need to start somewhere.  I need to create a routine to query a SQL database to determine the next available appointment.  The database is comprised of a table that holds all currently scheduled appointment times and their appointment type.  The duration of the appointment is determined by the appointment type, therefore an ending time can be calculated for each appointment.  Obviously, this can be done fairly easily with SQL.  A separate table stores the starting time and ending time for the day's appointments.  I'm trying to figure out the most efficient method to find an open slot.  I can think of some clumsy type of looping, but wondered if there is some other method I'm not thinking of.  Any help would be appreciated.

Friday, October 26, 2018 6:22 PM

• User475983607 posted

This is the point you lost me.  Are you saying to populate an array with the day's start and end date, in other words populate empty appointment slots?  Subtracting the indexes of booked appointments and differences greater than 1 show gaps?

Let's say you have two appointments.  Appointment one is from 10:00am to 10:30am.  The second appointment is from 11:00am to 12:00.  Mathematically, the time gap between Appointment one and two is the start date of Appointment two minus the end date of Appointment one; 11:00am-10:30am = 30 minutes.

You must write code to format a result set so that you can find the gap between appointments because the start and end dates are in different records.  Keep in mind the records must be sorted as it is unlikely the appointment records are inserted in order by date.   If you are dealing with multiple calendars, you'll need to keep that in mind too.

Here is a basic idea using SQL.  I simply offset the ID by one to line get the start and end date of the next record in one.

```IF OBJECT_ID('tempdb..#Appointment') IS NOT NULL
DROP TABLE #Appointment

CREATE TABLE #Appointment (
AppointmentID	INT	PRIMARY KEY IDENTITY(1,1),
StartDate		DATETIME,
EndDate			DATETIME
)

INSERT INTO #Appointment(StartDate, EndDate)
VALUES('2018-10-26 08:00:00.000', '2018-10-26 09:00:00.000'),
('2018-10-26 09:00:00.000', '2018-10-26 11:00:00.000'),
('2018-10-26 11:00:00.000', '2018-10-26 13:00:00.000'),
('2018-10-26 15:00:00.000', '2018-10-26 17:00:00.000')

SELECT StartDate, EndDate, DATEDIFF(hour, EndDate, StartDate)
FROM (
SELECT AppointmentID, EndDate
FROM #Appointment
) AS a
JOIN (
SELECT AppointmentID-1 as AppointmentID, StartDate
FROM #Appointment
) as b ON a.AppointmentID = b.AppointmentID
```

I used an Identity column to order the records. Obviously, this will not work in a real solution as you'll need to create a sequence without breaks but it does show one way to solve the issue.

Another solution is using ADO.NET to read the records into an object and doing calculation using a collection in C#.  Yet another idea is to create calendar's as suggested in my first post.

• Marked as answer by Thursday, October 7, 2021 12:00 AM
Monday, October 29, 2018 2:40 PM

All replies

• User-821857111 posted

I moved this from the C# forum since it seems to be a SQL question, but you say you can do the SQL, so what exactly are you after? Why do you want a C# solution instead of a SQL solution (which will most likely perform much better)?

Friday, October 26, 2018 7:20 PM
• User1122355199 posted

Hi,

I'm afraid you didn't really read/understand my post.  The first part of obtaining the appointment list and calculating and appointment duration time can be achieved through SQL.  I have no idea how to find available appointments wither through SQL or C#.

Friday, October 26, 2018 7:37 PM
• User-821857111 posted

Oh, I read it. I just didn't understand it, which is why I asked for some clarification so that I can either attempt to provide an answer or move the post to the correct location. It would help if you provided some detail on the schema of the relevant database table.

Friday, October 26, 2018 7:50 PM
• User475983607 posted

I would craft a DB design that has a calendar of operational days and hours.  For example, the office is open from 8am to 5pm Monday through Friday excluding holidays.  Minimum appointment is 30 minutes.

Using these requirements, populate a table where each record represents 30 minutes.  Monday 10/29/2018 will have 18 records.  Simply populate this table for the next X months or years.  Then when you schedule an appointment just check off the records.  If you have an appointment on 10/29/2018 from 10am-11:30am then just update the calendar table by setting the appointment ID column.

This design makes it very easy to find the next appointment from some variable start date programmatically.   All you have to do is

```SELECT Min(StartTime)
FROM Calendar
WHERE AppointmentId Is NULL
AND StartTime >= @StartTime```

If you want to find the next X hours open slot, you'll need to write a CTE.

If you are asking how to handle this with your current design then we'll need details on the table schema with sample data.

Friday, October 26, 2018 8:04 PM
• User1122355199 posted

Thanks for the response.  My current design utilizes the two tables you suggested, however, rather than preloading the appointment table with available appointments, I adopted the approach of the table storing only appointments made.  Part of the reason for this is that the appointments are variable in length, opening and closing dates are seasonal and subject to change, and the number of service providers varies daily.  I think DayPilot and some of the other open source solutions use the approach you are suggesting.  My thinking was that formatting a schedule in advance did not provide sufficient fluidity.  So for example, one table holds the opening and closing time for Mondays in October of 8:30 am to 5:00 pm.  Tuesday in October is from 11:00 am to 9:00 pm.  Appointments can be anywhere from 10 minutes to 45 minutes.  So I took the approach of the appointments table only storing appointments made rather than storing all available appointments.

Friday, October 26, 2018 8:34 PM
• User475983607 posted

Thanks for the response.  My current design utilizes the two tables you suggested, however, rather than preloading the appointment table with available appointments, I adopted the approach of the table storing only appointments made.  Part of the reason for this is that the appointments are variable in length, opening and closing dates are seasonal and subject to change, and the number of service providers varies daily.  I think DayPilot and some of the other open source solutions use the approach you are suggesting.  My thinking was that formatting a schedule in advance did not provide sufficient fluidity.  So for example, one table holds the opening and closing time for Mondays in October of 8:30 am to 5:00 pm.  Tuesday in October is from 11:00 am to 9:00 pm.  Appointments can be anywhere from 10 minutes to 45 minutes.  So I took the approach of the appointments table only storing appointments made rather than storing all available appointments.

Again, we need the table layout and sample data.  Otherwise, we're just guessing.

If the design has a table with start and end dates then you need to subtract the start date form the end date of the previous record.  You can do this is SQL or in C#.  If you do this in C# I would populate an array or multi dimensional array depending on what you feel is easiest.  Then subtract one index from the other.  Any positive values is a gap in time.  Essentially, you are crafting the calendar on the fly.

Friday, October 26, 2018 9:50 PM
• User1122355199 posted

Thanks for the response.  Here is a sample of the appointment data:

```ApptDateTime		ApptType
2018-10-29 08:50:00.000	WC
2018-10-29 09:20:00.000	FU
2018-10-29 09:40:00.000	FU
2018-10-29 10:00:00.000	FU
2018-10-29 10:20:00.000	WC
2018-10-29 10:50:00.000	WC
2018-10-29 11:20:00.000	FU
2018-10-29 11:40:00.000	WC
2018-10-29 14:20:00.000	FU
2018-10-29 15:20:00.000	WC
2018-10-29 15:40:00.000	WC
2018-10-29 16:00:00.000	FU             ```

This can be converted through C# to:

```ApptDateTime		ApptEnd			ApptType
2018-10-29 08:50:00.000	2018-10-29 09:10:00.000	WC
2018-10-29 09:20:00.000	2018-10-29 09:30:00.000	FU
2018-10-29 09:40:00.000	2018-10-29 09:50:00.000	FU
2018-10-29 10:00:00.000	2018-10-29 10:10:00.000	FU
2018-10-29 10:20:00.000	2018-10-29 10:40:00.000	WC
2018-10-29 10:50:00.000	2018-10-29 11:10:00.000	WC
2018-10-29 11:20:00.000	2018-10-29 11:30:00.000	FU
2018-10-29 11:40:00.000	2018-10-29 12:00:00.000	WC
2018-10-29 14:20:00.000	2018-10-29 14:30:00.000	FU
2018-10-29 15:20:00.000	2018-10-29 15:40:00.000	WC
2018-10-29 15:40:00.000	2018-10-29 16:00:00.000	WC
2018-10-29 16:00:00.000	2018-10-29 16:10:00.000	FU  ```

If you do this in C# I would populate an array or multi dimensional array depending on what you feel is easiest.  Then subtract one index from the other.  Any positive values is a gap in time.  Essentially, you are crafting the calendar on the fly.

This is the point you lost me.  Are you saying to populate an array with the day's start and end date, in other words populate empty appointment slots?  Subtracting the indexes of booked appointments and differences greater than 1 show gaps?

Sunday, October 28, 2018 10:41 PM
• User475983607 posted

This is the point you lost me.  Are you saying to populate an array with the day's start and end date, in other words populate empty appointment slots?  Subtracting the indexes of booked appointments and differences greater than 1 show gaps?

Let's say you have two appointments.  Appointment one is from 10:00am to 10:30am.  The second appointment is from 11:00am to 12:00.  Mathematically, the time gap between Appointment one and two is the start date of Appointment two minus the end date of Appointment one; 11:00am-10:30am = 30 minutes.

You must write code to format a result set so that you can find the gap between appointments because the start and end dates are in different records.  Keep in mind the records must be sorted as it is unlikely the appointment records are inserted in order by date.   If you are dealing with multiple calendars, you'll need to keep that in mind too.

Here is a basic idea using SQL.  I simply offset the ID by one to line get the start and end date of the next record in one.

```IF OBJECT_ID('tempdb..#Appointment') IS NOT NULL
DROP TABLE #Appointment

CREATE TABLE #Appointment (
AppointmentID	INT	PRIMARY KEY IDENTITY(1,1),
StartDate		DATETIME,
EndDate			DATETIME
)

INSERT INTO #Appointment(StartDate, EndDate)
VALUES('2018-10-26 08:00:00.000', '2018-10-26 09:00:00.000'),
('2018-10-26 09:00:00.000', '2018-10-26 11:00:00.000'),
('2018-10-26 11:00:00.000', '2018-10-26 13:00:00.000'),
('2018-10-26 15:00:00.000', '2018-10-26 17:00:00.000')

SELECT StartDate, EndDate, DATEDIFF(hour, EndDate, StartDate)
FROM (
SELECT AppointmentID, EndDate
FROM #Appointment
) AS a
JOIN (
SELECT AppointmentID-1 as AppointmentID, StartDate
FROM #Appointment
) as b ON a.AppointmentID = b.AppointmentID
```

I used an Identity column to order the records. Obviously, this will not work in a real solution as you'll need to create a sequence without breaks but it does show one way to solve the issue.

Another solution is using ADO.NET to read the records into an object and doing calculation using a collection in C#.  Yet another idea is to create calendar's as suggested in my first post.

• Marked as answer by Thursday, October 7, 2021 12:00 AM
Monday, October 29, 2018 2:40 PM
• User1122355199 posted

Thanks for the response.  I had to ponder your example for a bit and its intriguing, but I can't envision how this will work since it identifies the gaps in the schedule, but not the incremental appointment slots.  I guess that could be calculated.  I'm playing around with populating a complete list of available and scheduled appointments and then perhaps use a lambda expression to identify available slots.  My concern is that even if this works that it might be a very inefficient method to solve this problem.

I guess the other consideration is to redesign the database to store all possible appointments within a range of time.  That has always seemed to be a waste of resources as well as creating potential problems in the event schedule format changes.  Any input on how some of the commercial applications handle this problem.  The appointments only solutions has worked well for this application with the exception of this problem.

Wednesday, October 31, 2018 1:14 AM
• User1122355199 posted

Thanks for the ideas.  I'm close to a solution.  Will post when it is fully working.

Wednesday, November 7, 2018 1:46 AM