You don't do it that way: you create a couple of tables instead.
The first table holds the students:
ID Can be INT, IDENTITY (that way SQL will deal with ensuring it is unique), PRIMARY KEY
Name NVARCHAR(50) shoudl be fine
The second table holds attendance:
ID INT, IDENTITY (To make sure each row is unique), PRIMARY KEY
StudentID INT, FOREIGN KEY (Relates back to the actual Students table)
Attended DATE (Date they attended)
Then for a student attending, you create a new row in the second table which refers to the student from the first table, and logs the date they were present.
You then use WHERE and an SQL JOIN to retrieve the records you are interested in.