IF ((SELECT COUNT(CAST(StudentuserID AS int)) FROM StudentAttendance WHERE StudentUserID=1)>0)
PRINT 'Yes'
ELSE
PRINT 'No'

IF ((SELECT COUNT(CAST(StudentuserID AS int)) FROM StudentAttendance WHERE StudentUserID=1)>0)
UPDATE StudentAttendance
SET
CID = CAST('[querystring:CID]' AS int),
CalendarEventID = CAST('[querystring:CEID]' AS int),
StudentUserID = CAST('[StudentUserID]' AS int),
Attendance = '[Attendance]'
ELSE
INSERT INTO StudentAttendance
(CID,CalendarEventID,StudentUserID,Attendance)
VALUES
(CAST('[querystring:CID]' AS int), CAST('[querystring:CEID]' AS int), CAST('[StudentsUserID]' AS int),'[Attendance]')