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]});
        }
    }
}