Finding a date gap (missing date range) within a SQL table - sql-server

Question

On this SQL Server 2008 database I have a table of attendance, students come into school every day and check in, the table looks something like this:
SchoolID | StudentID | Date
There will be a record for every day for every student on this table. What I want to find out is, given a start date, an end date, and a number of days (gap), find any student that has not checked into school for that number of days. So for example, I need to know which students missed 3 days straight during the month of December, and spit out the list of StudentIDs.
How can I accomplish something like that?

Answer 1

You can produce date ranges from startdate to enddate
then outer join this data with your table, if the student wouldn't have come consider it as 1 then summarize this data.
for generating date range you can use this function as below
CREATE FUNCTION [dbo].[DateRange]
(
#Increment CHAR(1),
#StartDate DATETIME,
#EndDate DATETIME
)
RETURNS
#SelectedRange TABLE
(IndividualDate DATETIME)
AS
BEGIN
;WITH cteRange (DateRange) AS (
SELECT #StartDate
UNION ALL
SELECT
CASE
WHEN #Increment = 'd' THEN DATEADD(dd, 1, DateRange)
WHEN #Increment = 'w' THEN DATEADD(ww, 1, DateRange)
WHEN #Increment = 'm' THEN DATEADD(mm, 1, DateRange)
END
FROM cteRange
WHERE DateRange <=
CASE
WHEN #Increment = 'd' THEN DATEADD(dd, -1, #EndDate)
WHEN #Increment = 'w' THEN DATEADD(ww, -1, #EndDate)
WHEN #Increment = 'm' THEN DATEADD(mm, -1, #EndDate)
END)
INSERT INTO #SelectedRange (IndividualDate)
SELECT DateRange
FROM cteRange
OPTION (MAXRECURSION 3660);
RETURN
END
GO
then
select sum(isAbsent) absentDays, s.studentid from
(
select case when studentid is null then 1 else 0 end isAbsent,individualDate,s.studentid from DateRange('d', '01/11/2014', '30/11/2014') d
cross join tblstudent s
left outer join yourtable on yourtable.Date = d.IndividualDate and yourtable.studentid = s.studentid
) x
group by s.studentid
having sum(isAbsent) > 3

Answer 2

Just look at this. I think you will be able to figure out you own answer from that.This solution take care of the weekend days and holidays :
SQL Fiddle
MS SQL Server 2008 Schema Setup:
CREATE TABLE attendance
([SchoolID] int, [StudentID] int, [Date] datetime)
;
INSERT INTO attendance
([SchoolID], [StudentID], [Date])
VALUES
(1, 1, '2014-12-01 00:00:00'),
(1, 1, '2014-12-02 00:00:00'),
(1, 1, '2014-12-03 00:00:00'),
(1, 1, '2014-12-04 00:00:00'),
(1, 1, '2014-12-05 00:00:00'),
(1, 1, '2014-12-08 00:00:00'),
(1, 1, '2014-12-09 00:00:00'),
(1, 1, '2014-12-10 00:00:00'),
(1, 1, '2014-12-11 00:00:00'),
(1, 1, '2014-12-12 00:00:00'),
(1, 1, '2014-12-15 00:00:00'),
(1, 1, '2014-12-16 00:00:00'),
(1, 1, '2014-12-17 00:00:00'),
(1, 1, '2014-12-18 00:00:00'),
(1, 1, '2014-12-19 00:00:00'),
(1, 2, '2014-12-01 00:00:00'),
(1, 2, '2014-12-02 00:00:00'),
(1, 2, '2014-12-08 00:00:00'),
(1, 2, '2014-12-09 00:00:00'),
(1, 2, '2014-12-10 00:00:00'),
(1, 2, '2014-12-11 00:00:00'),
(1, 2, '2014-12-12 00:00:00'),
(1, 2, '2014-12-15 00:00:00'),
(1, 2, '2014-12-16 00:00:00'),
(1, 2, '2014-12-17 00:00:00'),
(1, 2, '2014-12-18 00:00:00'),
(1, 2, '2014-12-19 00:00:00')
;
CREATE TABLE holidays
([Date] datetime)
;
INSERT INTO holidays
([Date])
VALUES
('2014-12-22 00:00:00'),
('2014-12-23 00:00:00'),
('2014-12-24 00:00:00'),
('2014-12-25 00:00:00'),
('2014-12-26 00:00:00'),
('2014-12-29 00:00:00'),
('2014-12-30 00:00:00'),
('2014-12-31 00:00:00')
;
CREATE TABLE students
([StudentID] int, [Name] varchar(5))
;
INSERT INTO students
([StudentID], [Name])
VALUES
(1, 'John'),
(2, 'Peter')
;
Query 1:
DECLARE #start DATE, #end DATE
SELECT #start = '20141201', #end = '20141231'
;WITH tdate AS
(
SELECT TOP (DATEDIFF(DAY, #start, #end) + 1)
n = ROW_NUMBER() OVER (ORDER BY [object_id])
FROM sys.all_objects
)
SELECT DISTINCT Name
FROM students s
INNER JOIN attendance a ON s.StudentID = a.StudentID
INNER JOIN tdate ON DATEADD(DAY, n-1, #start) = a.Date
GROUP BY NAME
HAVING
(SELECT count(*)
FROM tdate
LEFT OUTER JOIN holidays h ON DATEADD(DAY, n-1, #start) = h.Date
WHERE h.date is null
AND DATEPART(dw,DATEADD(DAY, n-1, #start)) not in (1,7))
- COUNT(*) >= 3
Results:
| NAME |
|-------|
| Peter |
UPDATE
SELECT s.StudentID, d.Date
FROM students s
INNER JOIN (
SELECT DATEADD(DAY, n-1, #start) as Date
FROM tdate
LEFT OUTER JOIN holidays h ON DATEADD(DAY, n-1, #start) = h.Date
WHERE h.date is null
AND DATEPART(dw,DATEADD(DAY, n-1, #start)) not in (1,7)) d ON 1 = 1
LEFT OUTER JOIN attendance a ON s.StudentID = a.StudentID AND d.Date = a.Date
WHERE a.StudentID IS NULL
ORDER BY s.StudentID, d.Date
Results:
| STUDENTID | DATE |
|-----------|------------|
| 2 | 2014-12-03 |
| 2 | 2014-12-04 |
| 2 | 2014-12-05 |