代碼如下:
using System;
using System.Collections;
using System.Collections.Specialized;
using System.Data;
using System.Data.OracleClient;
using System.Configuration;
using System.Data.Common;
using System.Collections.Generic;

    /// <summary>
    /// 數據訪問抽象基礎類
    ///
    /// </summary>
public class DBBase
{

    //數據庫連接字符串(web.config來配置)，可以動態更改connectionString支持多數據庫.       
    public static string connectionString = System.Configuration.ConfigurationManager.ConnectionStrings["ConnectionString1"].ToString();
    public DBBase()
    {
    }

    #region 檢查用戶名是否存在
    /// <summary>
    /// 檢查用戶名是否存在，存在返回true，不存在返回false
    /// </summary>
    /// <param name="strSql"></param>
    /// <returns></returns>
    public static bool Exists(string strSql)
    {

        using (OracleConnection connection = new OracleConnection(connectionString))
        {
            connection.Open();
            OracleCommand myCmd = new OracleCommand(strSql, connection);
            try
            { 
                object obj = myCmd.ExecuteScalar(); //返回結果的第一行一列
                myCmd.Parameters.Clear();
                if ((Object.Equals(obj, null)) || (Object.Equals(obj, System.DBNull.Value)))
                {
                    return false;
                }
                else
                {
                    return true;
                }