Get Last and Next Appointments - sql

Question

I have the following table in SQL Server and would like to get the last and next appointments for each customer.
Note: If the first appointment is in the future, last appointment should be N/A. Similarly if the last appointment is in the past, next appointment will be N/A. If the last appointment is older than 30 days it should not be shown (if there is no future appointment - considered an inactive customer).
CustomerId (int) | Date (date) | Time (time)
1 | 20210801 | 11:00
1 | 20210802 | 13:00
1 | 20210805 | 10:00
1 | 20210811 | 16:00
1 | 20210821 | 17:00
2 | 20210801 | 11:00
2 | 20210802 | 11:00
2 | 20210803 | 11:00
2 | 20210804 | 11:00
3 | 20210831 | 11:00
4 | 20210526 | 10:00
In this case the result should be (Assuming the date is today 7 August 2021):
CustomerId (int) | LastAppointment (varchar) | NextAppointment (varchar)
1 | 05 Aug 2021 - 10:00 | 11 Aug 2021 - 16:00
2 | 04 Aug 2021 - 11:00 | N/A
3 | N/A | 31 Aug 2021 - 11:00
Can anyone help me please? An example would be appreciated.

Answer 1

You simply need to work with datetime values and then use conditional aggregation to select the required date for each customer. Using a CTE first to simplify converting the dates as much as possible, this looks like:
with ap as (
select CustomerId, Convert(datetime,Left(Concat([date], ' ', [time]),15)) app
from t
), groups as (
select CustomerId,
Max(case when app <= GetDate() then app end) LastAppointment,
Min(case when app > GetDate() then app end) NextAppointment
from ap
group by customerId
)
select CustomerID,
IsNull(Format(LastAppointment, 'dd MMM yyyy - hh:mm'), 'N/A') LastAppointment,
IsNull(Format(NextAppointment, 'dd MMM yyyy - hh:mm'), 'N/A') NextAppointment
from groups
where DateAdd(day,-30,GetDate()) < isnull(lastappointment,GetDate())
see DB<>Fiddle
Also note this query only touches the table once and performs a single logical read.

Answer 2

You need conditional aggregation:
SELECT CustomerId,
COALESCE(
MAX(CASE
WHEN CAST(Date AS DATETIME) + CAST(Time AS DATETIME) < GETDATE()
THEN FORMAT(CAST(Date AS DATETIME) + CAST(Time AS DATETIME), 'dd MMM yyyy - HH:mm')
END
), 'N/A'
) LastAppointment,
COALESCE(
MIN(CASE
WHEN CAST(Date AS DATETIME) + CAST(Time AS DATETIME) > GETDATE()
THEN FORMAT(CAST(Date AS DATETIME) + CAST(Time AS DATETIME), 'dd MMM yyyy - HH:mm')
END
), 'N/A'
) NextAppointment
FROM tablename
GROUP BY CustomerId
HAVING COALESCE(DATEDIFF(
d,
MAX(CASE
WHEN CAST(Date AS DATETIME) + CAST(Time AS DATETIME) < GETDATE()
THEN CAST(Date AS DATETIME) + CAST(Time AS DATETIME)
END
),
GETDATE()
), 0) < 30
See the demo.
Results:
CustomerId
LastAppointment
NextAppointment
1
05 Aug 2021 - 10:00
11 Aug 2021 - 16:00
2
04 Aug 2021 - 11:00
N/A
3
N/A
31 Aug 2021 - 11:00

Answer 3

NOTE : This solution works but it is very bad in terms of performance, check this answer for a better approach
Something like this
SELECT DISTINCT customerid,
Isnull(CONVERT(VARCHAR,
(SELECT TOP 1 Concat(date, ' ', TIME)
FROM appointments B
WHERE b.customerid = a.customerid
AND ([date] < CONVERT(DATE, Getdate())
OR ([date] = CONVERT(DATE, Getdate())
AND [time] <= CONVERT(TIME, Getdate())))
ORDER BY [date] DESC)), 'N/A') AS lastappointment,
Isnull(CONVERT(VARCHAR,
(SELECT TOP 1 Concat(date, ' ', TIME)
FROM appointments B
WHERE b.customerid = a.customerid
AND ([date] > CONVERT(DATE, Getdate())
OR ([date] = CONVERT(DATE, Getdate())
AND [time] > CONVERT (TIME, Getdate())))
ORDER BY [date])), 'N/A') AS nextappointment
FROM appointments A
WHERE Datediff(DAY,
(SELECT TOP 1 date
FROM appointments B
WHERE b.customerid = a.customerid
AND [date] <= CONVERT(DATE, Getdate())
ORDER BY [date] DESC), CONVERT(DATE, Getdate())) <= 30
OR (((
(SELECT TOP 1 date
FROM appointments B
WHERE b.customerid = a.customerid
AND [date] > CONVERT(DATE, Getdate())
ORDER BY [date]) > CONVERT(DATE, Getdate())))
OR ((
(SELECT TOP 1 date
FROM appointments B
WHERE b.customerid = a.customerid
AND [date] > CONVERT(DATE, Getdate())
ORDER BY [date]) = CONVERT(DATE, Getdate()))
AND (
(SELECT TOP 1 [time]
FROM appointments B
WHERE b.customerid = a.customerid
AND [date] > CONVERT(DATE, Getdate())
ORDER BY [date]) > CONVERT(TIME, Getdate()))))
I called your table appointments and the condition is to select customer with last appointment in the past 30 days OR with a future appointment.
I tested with column types Date for Date and Time(7) for time.

Answer 4

Base table is used only single time because of optimization purpose. Use LAG() function and others necessary condition for picking actual set of data.
-- SQL SERVER
SELECT p.CustomerId
, CASE WHEN p.chk_condition = 1
THEN CONVERT(varchar(13), p.prev_Date, 113) + ' - ' + LEFT(p.prev_time, 5)
WHEN p.chk_condition = 2
THEN CONVERT(varchar(13), p.Date, 113) + ' - ' + LEFT(p.time, 5)
ELSE 'N/A'
END "LastAppointment"
, CASE WHEN p.chk_condition != 2
THEN CONVERT(varchar(13), p.Date, 113) + ' - ' + LEFT(p.time, 5)
ELSE 'N/A'
END "NextAppointment"
FROM ( SELECT t.*
, CASE WHEN t.prev_Date < GETDATE() AND t.Date >= GETDATE()
THEN 1
WHEN t.prev_Date < GETDATE() AND t.Date <= GETDATE()
THEN 2
ELSE 0
END chk_condition
, ROW_NUMBER() OVER (PARTITION BY CustomerId ORDER BY t.Date DESC, t.prev_Date DESC) row_num
FROM (SELECT CustomerId, Date, Time
, LAG(Date) OVER (PARTITION BY CustomerId ORDER BY "Date", "Time") "prev_Date"
, LAG(Time) OVER (PARTITION BY CustomerId ORDER BY "Date", "Time") "prev_Time"
FROM appointment) t
WHERE CASE WHEN t.prev_Date < GETDATE() AND t.Date >= GETDATE()
THEN 1
WHEN t.prev_Date IS NULL
THEN CASE WHEN DATEDIFF(day, t.Date, GETDATE()) >= 30
THEN 0
ELSE 1
END
WHEN t.prev_Date < GETDATE() AND t.Date <= GETDATE()
THEN 1
END = 1 ) p
WHERE p.row_num = 1
ORDER BY p.CustomerId;
Please check this url https://dbfiddle.uk/?rdbms=sqlserver_2019&fiddle=3813d09cf25ed14d249970654995b085