Dim myConn As SqlConnection = New SqlConnection(strCon)
myConn.Open()
Dim strsql As String = "select * from 表 Where A字段='"+textbox控件1.text+"' and B字段='"+textbox控件1.text+"'"
Dim myCommand As New SqlCommand(strsql, myConn)
Dim myReader As SqlDataReader = myCommand.ExecuteReader()
Dim flag as boolean
if not myReader.Read() Then
flag=true
else
flag=false
end if
myReader.Close()
if flag=true then
//如果和表中某个记录的A和B字段都相同则修改C字段,