数据读取（SQL）与文本写入（fileStream）

要求：从三个不同服务器中取数，对最近10的历史数据进行去重，写出到文本。

1.读取。

 public static DataTable ExecuteSql(string connectString, string querySqlString)
         {
             DataTable dt = new DataTable();
             using (SqlConnection conn = new SqlConnection(connectString))
             {
                 conn.Open();
                 SqlCommand cmd = conn.CreateCommand();
                 cmd.CommandText = querySqlString;
                 using (SqlDataAdapter adapter = new SqlDataAdapter(cmd))
                 {
                     adapter.SelectCommand.CommandTimeout =  * ;
                     adapter.Fill(dt);
                     return dt;
                 }
             }
         }

当然，另外还有一种，定义了一个我要使用的类型，返回List<T>:

 public static List<MarketUrl> GetUrlListFromDataBase(string serverName, string sqlString)
         {
             List<MarketUrl> list = new List<MarketUrl>();
             MarketUrl mu = new MarketUrl();
             string connectStr = ConfigurationManager.ConnectionStrings[serverName].ConnectionString;
             using (SqlConnection conn = new SqlConnection(connectStr))
             {
                 conn.Open();
                 SqlCommand cmd = conn.CreateCommand();
                 cmd.CommandText = sqlString;
                 cmd.CommandTimeout =  * ;
                 SqlDataReader reader = cmd.ExecuteReader();
                 while (reader.Read())
                 {
                     var dr = new MarketUrl()
                     {
                         market = reader.GetString(reader.GetOrdinal("MarketCode")),
                         url = reader.GetString(reader.GetOrdinal("Url"))
                     };
                     list.Add(dr);
                 }
             }
             return list;
         }

2.去重（我的思路是，在取数的时候，对各自的data select 的时候先进行distinct，然后三个data merge到一起时，再次duplicate）：

 //colmuns 是distinct的 数组，为columnName
 public static DataTable GetDistinctRow(DataTable dt, string[] columns)
         {
             DataView dv = dt.DefaultView;
             DataTable dtDistinct = dv.ToTable(true, columns);
             return dtDistinct;
         }

3.DataRows ConvertTo DataTable

 //这是个额外用的到操作，先记下
 public static DataTable ConvertToDataTable(DataRow[] rows)
         {
             if (rows == null || rows.Count() < )
                 return null;
             DataTable dtResult = rows[].Table.Clone();
             foreach (DataRow r in rows)
             {
                 dtResult.Rows.Add(r.ItemArray);
             }
             return dtResult;
         }

4.写入到文本，因code还涉及到别的一些操作，这里只写最简单部分：

 StringBuilder sb = new StringBuilder();
 foreach (DataRow row in dt.Rows)
 {
       sb.AppendLine(dateString + " " + row[].ToString() + " " + row[].ToString());
 }
 using (FileStream fs = new FileStream(filePath, FileMode.Create, FileAccess.Write))
 7 {
      using (TextWriter tw = new StreamWriter(fs, Encoding.Default))
      {
          tw.Write(sb.ToString());
      }
 }
 File.WriteAllText(logPath, "[" + DateTime.UtcNow + "] Successed...\r\n");