主题：[求助]选择并复制记录问题

       有两个表：表A（10000条记录）和表B（2000条记录），主键均为  _Identify

       表B中有一个字段“编号”，类型为整形，存放从表A复制记录时的表A的_Identify的值

 当前主表是表B，在表B的主窗口中放置一个按钮（btn提取数据），点击按钮时，将表A的所有不在表B中的记录复制到表B中，

代码该怎么写？我下面的代码提示[查询超时已过期，未将对象引用到对象的实例]，用消息框看ids的值是空的

请老师看看有什么问题？

dim tb as table = e.form.controls("Table1").table

dim flt as string = ""

if tb.rows.count > 0 then

    dim ids as string

    for each r as row in tb.rows

        ids = ids & r("编号") & ","

    next

    flt = "[_Identify] not in (" & ids.trim(",") & ")"

endif

dim sCols() as string = {"_Identify","字段1","字段2","字段3"}

dim dCols() as string = {"编号","字段1","字段2","字段3"}

dim cmd as new sqlcommand

cmd.c

cmd.commandtext = "sel ect * from 表A where " & flt

dim dt as datatable = cmd.executereader()

for each dr as datarow in dt.datarows

    dim nr as datarow = tb.datatable.addnew()

    for i as integer = 0 to sCols.length-1

        nr(dCols(i)) = dr(sCols(i))

    next

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