主题：Executereader() 查询结果为空时返回什么呢?

ExecuteReader()返回值是DataReader型的（用来读取信息，一般用于查询语句，从表和视图中）

			
If e.DataCol.Name = 
"省市" Orelse e.DataCol.Name = "县市" Then
    
Dim cmd As New SQLCommand
    Dim dt 
As DataTable
    Dim dr As DataRow = e.DataRow
    cmd.C
    cmd.CommandText = "SELECT * From {行政区域} Where [省市] = '" & 
dr("省市") & 
"' And [县市] = '" & 
dr("县市") & 
"'" 
    
dt = cmd.ExecuteReader
    If dt.DataRows.Count > 0 Then
        dr("区号") = 
dt.DataRows(0)("区号")
        dr("邮编") = dt.DataRows(0)("邮编")
    Else
        
dr("区号") = 
Nothing
        dr("邮编") = Nothing
    End If