Adding Unique values to database

I have to add items to database, but need to make sure that one item is unique. what do i do here?

e.g lest say i need to add 100 rows of three columns each (school name idcard_num)

it is obvious that name should be unique here, while the rest can have duplicates

1 should i create a unique field , and spit out the database errors that will be thrown to the user?
2. should i check each items before adding?

i have this

Dim conn As New SQLiteConnection("Data Source=" & DBPath)
        'conn.SetPassword(dbPassword)
        conn.Open()
        Dim cmd As New SQLiteCommand(conn)
        Dim mytransaction As SQLiteTransaction = conn.BeginTransaction()
        Try


            '// insert courses //
            For i = 0 To UBound(oCourses)
                cmd = New SQLiteCommand("INSERT INTO courses ([code]," & _
                    "[title],[unit]) VALUES (@code,@title,@unit)", conn)
                cmd.Parameters.AddWithValue("@code", oCourses(i).Code)
                cmd.Parameters.AddWithValue("@title", oCourses(i).Title)
                cmd.Parameters.AddWithValue("@unit", oCourses(i).Unit)

                'Debug.Print(cmd.CommandText)
                cmd.ExecuteNonQuery()
              Next
            mytransaction.Commit()
            Return Nothing
        Catch ex As Exception
            mytransaction.Rollback()
            Debug.Print(ex.Message)
            Return ex.Message
        Finally
            cmd.Dispose()
            conn.Dispose()
            mytransaction.Dispose()
        End Try

Tags: Visual Basic, Sqlite, Windows Forms