主题：关于这段代码

Dim Cols1() As String = {"姓名"，"学籍号""学科","考试成绩"}

Dim Cols2() As String = {"姓名","学籍号""数学","考试成绩"}

For Each dr1 As DataRow In DataTables("总成绩").Select("[学科] = '数学' And [考试成绩] > 90")

    Dim dr2 As DataRow = DataTables("数学已及格").AddNew()

    For i As Integer = 0 To Cols1.Length -1

        dr2(Cols2(i)) = dr1(Cols1(i))

    Next

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第一个问题：如何实现排除重复值？第二个问题：对于表中已存在的数据将不进行填充