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I have created a database for students' attendance. I am facing an issue: if students scan their card twice there are two entries shown on the same day. I want one entry per day, and if someone tries twice then one entry should be deleted.

For this I have a table containing RFID numbers which are allocated to each student (this number is unique as well) and a auto current date & time when entry posted.

Now please suggest me how to stop the 2nd entry by coding as entry is done from a FORM which is directly connected with table. Thanks in advance.

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You should have one table with student information and one table in which you store the combination of the date and the primary key (your RFID i presume). Then you should define a Primary key on the new table, that consist of the date + RFID. Since this is your primary key this has to be unique, and scanning a card twice won't allow it to be entered twice.

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Dear Glenn i have done as per your statement given above. now system restrict me when doing the scanning twice. now what if i show the Error message on duplication ??? is this possible ??? – Muhammad Usman RAza Jun 9 at 10:57
The primary key constraint ensures uniqueness of the combined fields that form the primary key. Because of that database prevents you from adding another record with the same RFID/date combination. You need to handle the error in your application. – Ansgar Wiechers Jun 10 at 7:47

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