将两张DataTable进行join

        /// <param name="dt1">要合并的表一</param>
        /// <param name="dt2">要合并的表二</param>
        /// <param name="KeyColName">dt1与dt2联系的关键列名 </param>
        public DataTable MergeDataTable(DataTable dt1, DataTable dt2, String KeyColName)
        {
            //定义临时变量
            DataTable dtReturn = new DataTable();
            int i = 0;
            int j = 0;
            int k = 0;
            int l=0;
            int colKey1 = 0;
            int colKey2 = 0;

            //设定表dtReturn的名字
            dtReturn.TableName = dt1.TableName;
            //设定表dtReturn的列名
            for (i = 0; i < dt1.Columns.Count; i++)
            {
                if (dt1.Columns[i].ColumnName == KeyColName)
                {
                    colKey1 = i;
                }
                dtReturn.Columns.Add(dt1.Columns[i].ColumnName);
            }
            for (j = 0; j < dt2.Columns.Count; j++)
            {
                if (dt2.Columns[j].ColumnName == KeyColName)
                {
                    colKey2 = j;
                    continue;
                }
                dtReturn.Columns.Add(dt2.Columns[j].ColumnName);
            }
            //建立表的空间
            //int len = dt1.Rows.Count + dt2.Rows.Count;

            int len = dt1.Rows.Count;
            for (i = 0; i < dt2.Rows.Count; i++)
            {
                int v = -1;
                for (j = 0; j < dt1.Rows.Count; j++)
                {
                    string z = dt2.Rows[i][colKey1].ToString();
                    string x = dt1.Rows[j][colKey2].ToString();
                    if (dt2.Rows[i][colKey1].ToString() == dt1.Rows[j][colKey2].ToString())
                    {
                        v = 1;
                        break;
                    }
                }
                if (v == -1)
                {
                    len++;
                }
            }
                for (i = 0; i < len; i++)
                {
                    DataRow dr;
                    dr = dtReturn.NewRow();
                    dtReturn.Rows.Add(dr);
                }

            for (i = 0; i < dt1.Rows.Count; i++)
            {
                //表dt1的第i行数据拷贝到dtReturn中去
                for (j = 0; j < dt1.Columns.Count; j++)
                {
                    dtReturn.Rows[i][j] = dt1.Rows[i][j].ToString();
                }
            }
            int m = -1;
            int n=dt1.Rows.Count;
                //查找的dt2中KeyColName的数据,与dt1相同的行
            for (l = 0; l < dt2.Rows.Count; l++)
            {
                for (k = 0; k < dt1.Rows.Count; k++)
                {
                    string z = dt2.Rows[l][colKey1].ToString();
                    string x = dt1.Rows[k][colKey2].ToString();
                    if (dt2.Rows[l][colKey1].ToString() == dt1.Rows[k][colKey2].ToString())
                    {
                        m = k;
                        break;
                    }
                    else
                    {
                        m = -1;
                    }
                }
                //表dt2的第m行数据拷贝到dtReturn中去,且不要KeyColName(ID)列
                if (m != -1)
                {
                    string p = dt2.Rows[l][0].ToString();
                      dtReturn.Rows[m][2] = dt2.Rows[l][1].ToString();
                }
                else
                {
                      dtReturn.Rows[n][0]=dt2.Rows[l][0].ToString();
                      dtReturn.Rows[n][2] = dt2.Rows[l][1].ToString();
                      n++;
                }
            }
            return dtReturn;
        }