using System;
using System.Data;
using System.Text;namespace ConsoleApp
{class Program{static void Main(string[] args){DataTable dt = new DataTable("temp");dt.Columns.Add("Id");           //添加列dt.Columns.Add("Name");dt.Rows.Add("1", "刘备");       //添加行dt.Rows.Add("2", "关羽");dt.Rows.Add("3", "张飞");dt.Rows.Add("4", "赵云");dt.Rows.Add("5", "黄忠");SelectFun(dt);Console.ReadKey();}#region 遍历范例/// <summary>/// 遍历方式一/// </summary>/// <param name="dt"></param>static void TraversalFun1(DataTable dt){for (int i = 0; i < dt.Rows.Count; i++){Console.WriteLine("编号:{0};名称:{1}",dt.Rows[i]["Id"].ToString(),dt.Rows[i]["Name"].ToString());}}/// <summary>/// 遍历方式二/// </summary>/// <param name="dt"></param>static void TraversalFun2(DataTable dt){foreach (DataRow myRow in dt.Rows){Console.WriteLine("编号:{0};名称:{1}",myRow[0].ToString(),myRow[1].ToString());}}/// <summary>/// 遍历方式三/// </summary>/// <param name="dt"></param>static void TraversalFun3(DataTable dt){foreach (DataRow dr in dt.Rows){Console.WriteLine("编号:{0};名称:{1}",dr["Id"].ToString(),dr["Name"].ToString());}}/// <summary>/// 遍历方式四/// </summary>/// <param name="dt"></param>static void TraversalFun4(DataTable dt){StringBuilder msg = new StringBuilder();foreach (DataRow dr in dt.Rows){msg.Clear();foreach (DataColumn dc in dt.Columns){msg.AppendFormat("{0}:{1};", dc.ColumnName, dr[dc.ColumnName]);}Console.WriteLine(msg.ToString());}}#endregion#region 查找范例static void SelectFun(DataTable dt){//条件查询Console.WriteLine("条件查询示例语句:Id > 1 and Name <> '关羽'");Display(dt.Select("Id > 1 and Name <> '关羽'", "Id desc"));//like示例Console.WriteLine("like示例语句:Name like '关%");Display(dt.Select("Name like '关%'", "Id desc")); }static void Display(DataRow[] drArr){foreach (DataRow dr in drArr){Console.WriteLine(dr["Name"]);}}#endregion}
}

using System;
using System.Data;namespace ConsoleApp
{class Program{static void Main(string[] args){DataTable dt = new DataTable();dt.Columns.Add("Id");dt.Columns.Add("Name");dt.Columns.Add("Age", typeof(Int32));       //注意要计算平均值要设置列类型为数字dt.Rows.Add("1", "刘备", 31);dt.Rows.Add("2", "关羽", 29);dt.Rows.Add("3", "张飞", 28);dt.Rows.Add("4", "赵云", 27);dt.Rows.Add("5", "黄忠", 50);dt.DefaultView.Sort = "Age DESC";           //排序dt = dt.DefaultView.ToTable();foreach (DataRow dr in dt.Rows){Console.WriteLine(dr["Name"]);}object obj = dt.Compute("Count(Id)", "Age>26");     //输出3 查询年龄大于26的人数
            Console.WriteLine(obj.ToString());object obj2 = dt.Compute("Avg(Age)", "true");     //输出33 查询所有人的平均年龄(要设置列为整型，否则不能计算)
            Console.WriteLine(obj2.ToString());object obj3 = dt.Compute("Sum(Age)", "true");     //输出165
            Console.WriteLine(obj3.ToString());Console.ReadKey();}}
}

using System;
using System.Data;namespace ConsoleApp
{class Program{static void Main(string[] args){DataTable dt = new DataTable();DataColumn dc = dt.Columns.Add("Id", Type.GetType("System.Int32"));dc.AutoIncrement = true;    //自动增加dc.AutoIncrementSeed = 1;   //起始为1dc.AutoIncrementStep = 1;   //步长为1dc.AllowDBNull = false;     //不允许为空
dt.Columns.Add("Name", Type.GetType("System.String"));dt.Columns.Add("Age", typeof(Int32));       //注意要计算平均值要设置列类型为数字dt.Rows.Add(null, "刘备", 31);            //注意这次添加不用在手输Id了，但是要给个nulldt.Rows.Add(null, "关羽", 29);dt.Rows.Add(null, "张飞", 28);dt.Rows.Add(null, "赵云", 27);dt.Rows.Add(null, "黄忠", 50);foreach (DataRow dr in dt.Rows){Console.WriteLine(dr["Id"]);    //输出1 2 3 4 5
            }Console.ReadKey();}}
}

using System;
using System.Data;namespace ConsoleApp
{class Program{static void Main(string[] args){DataTable dt = new DataTable();dt.Columns.Add("Name", typeof(String));dt.Columns.Add("Age", typeof(Int32));dt.Rows.Add("撼地神牛", 0);dt.Rows.Add("刘备", 21);for (int i = 0; i < dt.Rows.Count; i++){if (dt.Rows[i]["Age"].ToString() == "0"){//dt.Rows[i]["Age"] = null;     这样写会提示如下错误：不能将 Column“Age”设置为 null。请改用 DBNull。dt.Rows[i]["Age"] = DBNull.Value;}Console.WriteLine(dt.Rows[i]["Name"] + ":" + dt.Rows[i]["Age"]);}Console.ReadKey();}}
}