DataTable相关操作，筛选，取前N条数据，获取指定列数据

#region DataTable筛选，排序返回符合条件行组成的新DataTable或直接用DefaultView按条件返回
/// <summary>
/// DataTable筛选，排序返回符合条件行组成的新DataTable或直接用DefaultView按条件返回
/// eg:SortExprDataTable(dt,"Sex='男'","Time Desc",1)
/// </summary>
/// <param name="dt">传入的DataTable</param>
/// <param name="strExpr">筛选条件</param>
/// <param name="strSort">排序条件</param>
/// <param name="mode">1,直接用DefaultView按条件返回,效率较高;2,DataTable筛选，排序返回符合条件行组成的新DataTable</param>
public static DataTable SortDataTable(DataTable dt, string strExpr, string strSort, int mode)
{
switch (mode)
{
case 1:
//方法一　直接用DefaultView按条件返回
dt.DefaultView.RowFilter = strExpr;
dt.DefaultView.Sort = strSort;
return dt;
case 2:
//方法二　DataTable筛选，排序返回符合条件行组成的新DataTable
DataTable dt1 = new DataTable();
DataRow[] GetRows = dt.Select(strExpr, strSort);
//复制DataTable dt结构不包含数据
dt1 = dt.Clone();
foreach (DataRow row in GetRows)
{
dt1.Rows.Add(row.ItemArray);
}
return dt1;
default:
return dt;
}
}
#endregion
#region 获取DataTable前几条数据
/// <summary>
/// 获取DataTable前几条数据
/// </summary>
/// <param name="TopItem">前N条数据</param>
/// <param name="oDT">源DataTable</param>
/// <returns></returns>
public static DataTable DtSelectTop(int TopItem, DataTable oDT)
{
if (oDT.Rows.Count < TopItem) return oDT;

DataTable NewTable = oDT.Clone();
DataRow[] rows = oDT.Select("1=1");
for (int i = 0; i < TopItem; i++)
{
NewTable.ImportRow((DataRow)rows[i]);
}
return NewTable;
}
#endregion

#region 获取DataTable中指定列的数据
/// <summary>
/// 获取DataTable中指定列的数据
/// </summary>
/// <param name="dt">数据源</param>
/// <param name="tableName">新的DataTable的名词</param>
/// <param name="strColumns">指定的列名集合</param>
/// <returns>返回新的DataTable</returns>
public static DataTable GetTableColumn(DataTable dt, string tableName, params string[] strColumns)
{
DataTable dtn = new DataTable();
if (dt == null)
{
throw new ArgumentNullException("参数dt不能为null");
}
try
{
dtn = dt.DefaultView.ToTable(tableName, true, strColumns);
}
catch (Exception e)
{
throw new Exception(e.Message);
}
return dtn;
}
#endregion