作者：浪漫十一狼
在下面的例子中实现了3个Join方法，其目的是把两个DataTable连接起来，相当于Sql的Inner Join方法，返回DataTable的所有列。
如果两个DataTable中的DataColumn有重复的话，把第二个设置为ColumnName+"_Second",下面是代码，希望对大家有所帮助。
using System;
using System.Data;

namespace WindowsApplication1
{
    public class SQLOps
    {
        public SQLOps()
        {           
        }

        public static DataTable Join (DataTable First, DataTable Second, DataColumn[] FJC, DataColumn[] SJC)

        {

            //创建一个新的DataTable

            DataTable table = new DataTable("Join");

            // Use a DataSet to leverage DataRelation

            using(DataSet ds = new DataSet())

            {

                //把DataTable Copy到DataSet中

                ds.Tables.AddRange(new DataTable[]{First.Copy(),Second.Copy()});

                DataColumn[] parentcolumns = new DataColumn[FJC.Length];

                for(int i = 0; i < parentcolumns.Length; i++)

                {

                    parentcolumns[i] = ds.Tables[0].Columns[FJC[i].ColumnName];

                }

                DataColumn[] childcolumns = new DataColumn[SJC.Length];

                for(int i = 0; i < childcolumns.Length; i++)

                {

                    childcolumns[i] = ds.Tables[1].Columns[SJC[i].ColumnName];

                }

                //创建关联

                DataRelation r = new DataRelation(string.Empty,parentcolumns,childcolumns,false);

                ds.Relations.Add(r);

                //为关联表创建列

                for(int i = 0; i < First.Columns.Count; i++)

                {

                    table.Columns.Add(First.Columns[i].ColumnName, First.Columns[i].DataType);

                }

                for(int i = 0; i < Second.Columns.Count; i++)

                {

                    //看看有没有重复的列，如果有在第二个DataTable的Column的列明后加_Second

                    if(!table.Columns.Contains(Second.Columns[i].ColumnName))

                        table.Columns.Add(Second.Columns[i].ColumnName, Second.Columns[i].DataType);

                    else

                        table.Columns.Add(Second.Columns[i].ColumnName + "_Second", Second.Columns[i].DataType);

                }
              

                table.BeginLoadData();

                foreach(DataRow firstrow in ds.Tables[0].Rows)

                {

                    //得到行的数据

                    DataRow[] childrows = firstrow.GetChildRows(r);

                    if(childrows != null && childrows.Length > 0)

                    {

                        object[] parentarray = firstrow.ItemArray;

                        foreach(DataRow secondrow in childrows)

                        {

                            object[] secondarray = secondrow.ItemArray;

                            object[] joinarray = new object[parentarray.Length+secondarray.Length];

                            Array.Copy(parentarray,0,joinarray,0,parentarray.Length);

                            Array.Copy(secondarray,0,joinarray,parentarray.Length,secondarray.Length);

                            table.LoadDataRow(joinarray,true);

                        }

                    }

                }

                table.EndLoadData();

            }

            return table;

        }

        public static DataTable Join (DataTable First, DataTable Second, DataColumn FJC, DataColumn SJC)

        {

            return Join(First, Second, new DataColumn[]{FJC}, new DataColumn[]{SJC});

        }

        public static DataTable Join (DataTable First, DataTable Second, string FJC, string SJC)

        {

            return Join(First, Second, new DataColumn[]{First.Columns[FJC]}, new DataColumn[]{First.Columns[SJC]});

        }

    }
}