在下面的例子中實現了3個join方法，其目的是把兩個datatable連接起來，相當于sql的inner join方法，返回datatable的所有列。
如果兩個datatable中的datacolumn有重復的話，把第二個設置為columnname+"_second",下面是代碼，希望對大家有所幫助。
using system;
using system.data;

namespace windowsapplication1
{
    public class sqlops
    {
        public sqlops()
        {           
        }
        public static datatable join (datatable first, datatable second, datacolumn[] fjc, datacolumn[] sjc)
        {
            //創建一個新的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];
                }

                //創建關聯
                datarelation r = new datarelation(string.empty,parentcolumns,childcolumns,false);
                ds.relations.add(r);

                //為關聯表創建列
                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++)
                {
                    //看看有沒有重復的列，如果有在第二個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)
                {
                    //得到行的數據
                    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]});
        }
    }
}