主题：提取科目编码前几位等于指定值

 Dim cmd As New SQ L Command
    Dim dt As DataTable
    cmd.Connect i
    Dim str As String = e.form.Controls("DropBox1").value
    Dim d1 = str.Length   
    cmd. CommandText = "Sel  ect  编制日期,凭证编码,凭证摘要,借方金额,贷方金额,科目名称,尾级名称 from {凭证明细} Where [编制日期] >= '" & e.For m.Controls("StartDate").Value & "' And [编制日期] <= '" & e.Form.Controls("EndDate").Value & "' And [科目编码].SubString(0,d1) = '" & e.Form.Controls("DropBox1").Value & "'"
    dt = cmd.ExecuteReader()

想提取科目编码前几位等于选定科目编码的明细。

[科目编码].SubString(0,d1) = '" & e.Form.Co ntrols("DropBox1").Value & "'"

这个需要怎样改呢