如何使用删除根据表中的最大日期从 Oracle 表中删除行？

Question

我正在尝试创建一个 SQL 语句，该语句允许我删除表中比最合适的日期更早的所有行，同时保留最新的。这被用于我正在从事的项目。我正在从 MS Access 数据库中获取数据并将该数据拖到 oracle 表中。该程序正在构建到我在 Visual Studio 2008 C# 中创建的 Windows 服务应用程序中，以便我可以让它定期运行以获取最新信息。

我只需要弄清楚一些要添加到我的代码中的东西：

1. 想办法从我的 Oracle 表中删除那些旧行

2. 告诉我的服务每隔一小时或两小时运行一次

3. 检查连接错误、丢失文件等。

对于我的主要问题和其他步骤的任何帮助将不胜感激。

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Diagnostics;
using System.Linq;
using System.ServiceProcess;
using System.Text;
using System.Data.OracleClient;
using System.Data.SqlClient;
using System.IO;
using System.Data.Odbc;

namespace GasReportservice
{
  public partial class GasReportService : ServiceBase
  {
    public GasReportService()
    {
        InitializeComponent();
        if (!System.Diagnostics.EventLog.SourceExists("MySource"))
        {
            System.Diagnostics.EventLog.CreateEventSource("MySource", "MyNewLog");
        }
        eventLog1.Source = "MySource";
        eventLog1.Log = "MyNewLog";
    }
    protected override void OnStart(string[] args)
    {
        eventLog1.WriteEntry("In OnStart");
        string connectionString = "Dsn=Gas_meter";
        string col0 = "";
        string col1 = "";
        string col2 = "";
        string col3 = "";
        string col4 = "";
        string col5 = "";
        string col6 = "";
        string col7 = "";
        string col8 = "";
        OdbcConnection DbConnection = new OdbcConnection(connectionString);
        OdbcCommand DbCommand = DbConnection.CreateCommand();
        DbConnection.Open();
        DbCommand.CommandText = "SELECT DateTime, S1Flow, S2Flow, S3Flow, S4Flow, S1FlowTotal, S2FlowTotal, S3FlowTotal, S4FlowTotal FROM CommonStation WHERE Format(DateTime, 'mm/dd/yyyy') >=(select Format(max(DateTime),'mm/dd/yyyy') from CommonStation)";
        OdbcDataReader DbReader = DbCommand.ExecuteReader();
        int fCount = DbReader.FieldCount;


        /*
        for (int i = 0; i < fCount; i++)
        {
                String fName = DbReader.GetName(i);
                Console.Write(fName + "\t");
        }
        */

        try
        {
            while (DbReader.Read())
            {
                string connString = "DSN=Gas_meter_proj;Uid=cm;Pwd=cmdev123";
                OdbcConnection conn = new OdbcConnection(connString);
                string sqlins = @"insert into Commonstation(CommStatDate_Time, S1_Flow, S2_Flow, S3_Flow, S4_Flow, S1_Flow_Total, S2_Flow_Total, S3_Flow_Total, S4_Flow_Total ) values (to_date('" + col0 + "', 'MM/DD/YYYY HH:MI:SS AM' ),to_number('" + col1 + "'), to_number('" + col2 + "'), to_number('" + col3 + "'), to_number('" + col4 + "'),to_number('" + col5 + "'),to_number('" + col6 + "'),to_number('" + col7 + "'),to_number('" + col8 + "'))";
                OdbcCommand cmdnon = new OdbcCommand(sqlins, conn);
                cmdnon.Parameters.Add(col0, OdbcType.DateTime);
                cmdnon.Parameters.Add(col1, OdbcType.Numeric);
                cmdnon.Parameters.Add(col2, OdbcType.Numeric);
                cmdnon.Parameters.Add(col3, OdbcType.Numeric);
                cmdnon.Parameters.Add(col4, OdbcType.Numeric);
                cmdnon.Parameters.Add(col5, OdbcType.Numeric);
                cmdnon.Parameters.Add(col6, OdbcType.Numeric);
                cmdnon.Parameters.Add(col7, OdbcType.Numeric);
                cmdnon.Parameters.Add(col8, OdbcType.Numeric);
                conn.Open();
                col0 = DbReader["DateTime"].ToString();
                col1 = DbReader["S1Flow"].ToString();
                col2 = DbReader["S2Flow"].ToString();
                col3 = DbReader["S3Flow"].ToString();
                col4 = DbReader["S4Flow"].ToString();
                col5 = DbReader["S1FlowTotal"].ToString();
                col6 = DbReader["S2FlowTotal"].ToString();
                col7 = DbReader["S3FlowTotal"].ToString();
                col8 = DbReader["S4FlowTotal"].ToString();

                int rowsAffected = cmdnon.ExecuteNonQuery();

                conn.Close();
                Console.WriteLine(rowsAffected);                                   
            }
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.ToString());
        }
        finally
        {
            DbReader.Close();
            DbCommand.Dispose();
            DbConnection.Close();
        }

    }

    protected override void OnContinue()
    {
        eventLog1.WriteEntry("My service has resumed action.");
    }

    protected override void OnPause()
    {
        eventLog1.WriteEntry("My service has been paused.");
    } 

    protected override void OnStop()
    {
        eventLog1.WriteEntry("My service has been stopped.");
    }
  }
}

Answer 1

这是基本的 SQL。

DELETE FROM <yourtable> 
  WHERE <yourdatefield> < (SELECT Max(<yourdatefield>) FROM <yourtable>)

对于您的其他观点，它们应该是单独的问题。它们是完全不同的主题，应该独立于这个主题来回答（和搜索）。