var list=dt2.AsEnumerable().Except(dt1.AsEnumerable());
DataTable resultDt;
if(list.Count()>0)
    resultDt=list.CopyToDataTable();
else
    resultDt=dt2.Clone();//克隆個結(jié)構(gòu)；

void Main()
{
	Stopwatch sw = new Stopwatch();
	sw.Start();
	var dt1 = CreateDt(500000, 3);
	var dt2 = CreateDt(600000, 5);
	sw.Stop();
	sw.Elapsed.Dump("生成兩個表的時間");
	
	sw.Restart();
	//dt2.AsEnumerable().Except(dt1.AsEnumerable());//如果表格表的結(jié)構(gòu)相同，則直接差集處理得出結(jié)果
	var dt = dt2.AsEnumerable().Join(dt1.AsEnumerable(), p => p[0], p => p[0], (p, q) => p);//內(nèi)連接，查詢兩個表格相同部分，再利用相同部分做差集處理得出結(jié)果就是dt2在dt1中的差集
	var result = dt2.AsEnumerable().Except(dt).ToList();
	sw.Stop();
	result.Count.Dump("差集結(jié)果條數(shù)");
	sw.Elapsed.Dump("查詢差異的時間");
	sw.Restart();
	DataTable resultDt;
	if (result.Count() > 0)
	resultDt = result.CopyToDataTable();
	else
		resultDt = dt2.Clone();
	
	sw.Stop();
	sw.Elapsed.Dump("轉(zhuǎn)成DataTable耗時：");
 
}
DataTable CreateDt(int row, int count)
{
	var dt = new DataTable();
	for (int i = 0; i < count; i++)
		dt.Columns.Add("col" + i);
	var rnd = new Random();
	for (int i = 0; i < row; i++)
	{
		var num = rnd.Next(0, row);
		dt.Rows.Add(dt.Columns.Cast<DataColumn>().Select(p => p.ColumnName + num).ToArray());
	}
	return dt;
}