如何防止显示全部上机学生时重复

在做机房收费系统查看学生上机状态中，显示全部信息时，发现会出现重复的卡号，后来查了又查，改了又改，加了个简单的循环，便避免了这种情况

Private Sub showAll_Click()    Dim txtsqlOn As String    Dim msgtext As String    Dim mrcOn As ADODB.Recordset    Dim i As Integer    Dim j As Integer    txtsqlOn = "select * from online_info"    Set mrcOn = executeSQL(txtsqlOn, msgtext)        With myFlexGrid        .CellAlignment = 4        .Rows = 1        .TextMatrix(0, 0) = "卡号"        .TextMatrix(0, 1) = "姓名"        .TextMatrix(0, 2) = "上机日期"        .TextMatrix(0, 3) = "上机时间"        .TextMatrix(0, 4) = "机房号"        Do While Not mrcOn.EOF            .CellAlignment = 4            .Rows = .Rows + 1            .TextMatrix(.Rows - 1, 0) = mrcOn!cardno            .TextMatrix(.Rows - 1, 1) = mrcOn!studentname            .TextMatrix(.Rows - 1, 2) = mrcOn!ondate            .TextMatrix(.Rows - 1, 3) = mrcOn!OnTime            .TextMatrix(.Rows - 1, 4) = mrcOn!computer            mrcOn.MoveNext            For i = 0 To .TextMatrix(.Rows - 1, 0)          '  .Rows = .Rows + 1                For j = j + 1 To Val(Trim(.TextMatrix(.Rows - 1, 0)))                If .TextMatrix(i, 0) = .TextMatrix(j, 0) Then                    .RemoveItem j                    Exit Sub                Else                                End If            Next j        Next i        Loop    End WithEnd Sub