Select Distinct on DataTable

当你有一天你厌烦了访问数据库
这时候你也许会碰到以前没有的问题
你获得的DataTable中有重复的数据
于是
  public class DataSetHelper
    {     
        public DataSet ds;
        public DataSetHelper(ref DataSet DataSet)
        {
            ds = DataSet;
        }
        public DataSetHelper()
        {
            ds = null;
        }
        private static bool ColumnEqual(object A, object B)
        {         
            if (A == DBNull.Value && B == DBNull.Value)
                return true;
            if (A == DBNull.Value || B == DBNull.Value)
                return false;
            return (A.Equals(B));
        }
        //新表名,原表,作用的字段名 返回新表
        public static DataTable SelectDistinct(string TableName, DataTable SourceTable, string FieldName)
        {
            DataTable dt = new DataTable(TableName);
            dt.Columns.Add(FieldName, SourceTable.Columns[FieldName].DataType);

            object LastValue = null;
            foreach (DataRow dr in SourceTable.Select("", FieldName))
            {
                if (LastValue == null || !(ColumnEqual(LastValue, dr[FieldName])))
                {
                    LastValue = dr[FieldName];
                    dt.Rows.Add(new object[] { LastValue });
                }
            }
            if (ds != null)
                ds.Tables.Add(dt);
            return dt;
        }
    }