C#中的DataTable查詢實戰教程

DataTable dt = dataBox.GetDataForDataTable();//獲取DataTable所有數據，準備進行查詢
DataRow[] dtRow = dt.Select("調劑日期=‘"+MediumCode.Text.Trim()+"'");//根據查詢條件，篩選出所有滿足條件的列
DataTable dtNew = dt.Clone();//克隆與原表結構相同的新表(不包括數據)
foreach (DataRow item in dtRow)//把滿足條件的所有列賽到新表中
{
  dtNew.ImportRow(item);
}
dataBox.DataBinding(dtNew);//給控件綁定新值(即查詢結果)

var query = from g in dt_stu.AsEnumerable()
				  group g by new { 
					  t1 = g.Field<string>("STU_ID"), 
					  t2 = g.Field<string>("CLASS_ID")
				  } into m
			select new
			{
				STU_ID = m.Key.t1,
				CLASS_ID=m.Key.t2,
				成績總合計 = m.Sum(a => a.Field<decimal>("成績")),
				優秀人數 = m.Count(a => a.Field<decimal>("成績")>95)
			};
DataTable dt_article = UserClass.ToDataTable(query); 
 
/// <summary>
/// LINQ返回DataTable類型
/// </summary>
/// <typeparam name="T"> </typeparam>
/// <param name="varlist"> </param>
/// <returns> </returns>
public static DataTable ToDataTable<T>(IEnumerable<T> varlist)
{
	DataTable dtReturn = new DataTable();
 
	// column names
	PropertyInfo[] oProps = null;
 
	if (varlist == null)
		return dtReturn;
 
	foreach (T rec in varlist)
	{
		if (oProps == null)
		{
			oProps = ((Type)rec.GetType()).GetProperties();
			foreach (PropertyInfo pi in oProps)
			{
				Type colType = pi.PropertyType;
 
				if ((colType.IsGenericType) && (colType.GetGenericTypeDefinition()
				== typeof(Nullable<>)))
				{
					colType = colType.GetGenericArguments()[0];
				}
 
				dtReturn.Columns.Add(new DataColumn(pi.Name, colType));
			}
		}
 
		DataRow dr = dtReturn.NewRow();
 
		foreach (PropertyInfo pi in oProps)
		{
			dr[pi.Name] = pi.GetValue(rec, null) == null ? DBNull.Value : pi.GetValue
			(rec, null);
		}
 
		dtReturn.Rows.Add(dr);
	}
	return dtReturn;
}