>I have "student.dbf" with field 1.regno 2.applno 3. Name 4.course.
>How to prevent duplicate entry when i entering data entry? for example the applno "21005" is already exists in my table, by mistakenly again I enter same applno the message box tell record already exist, Do you want to continue is yes mean allow or if no means clear text boxes value.
>
> How to do this?

1. There should be an index in your table - either primary or candidate to exclude duplicates on the table's level

2. You can use seek or Select-SQL to verify that entered value doesn't already exist in a table.