整个例子的完整代码如下，VS2008下编译测试通过，本人已通过它实现N个项目，欢迎大家评测，谢谢指教

publicenum DBType
...{
       Access,
       SQL,
       DB2,
       Oracle,
       MySQL
   }

publicinterface IDBAccess
...{
void Init(string strServer, string strDataBase, string strUser, string strPwd);
void Open();
void Close();
bool TestConn();
int RunNoQuery(string strCmd);
       DataTable RunQuery(string strCmd);
       DBType DBType ...{ get;}
int GetFiledMax(string strTable, string strField);
       DataTable Tables ...{ get; }
       DataTable GetColumns();
       DataTable GetColumns(string strTable);
   }

publicstaticclass DBAccessFactory
...{
publicstatic IDBAccess Create(DBType type)
...{
           IDBAccess IRet = null;
switch (type)
...{
case DBType.Access:
                   IRet = new Access(type);
break;

case DBType.SQL:
                   IRet = new SQL(type);
break;

default:
break;
           }
return IRet;
       }

privateabstractclass DBAccess : IDBAccess
...{
protected DbConnection m_oConn = null;
protectedconststring CON_strServer = "Server";
protectedconststring CON_strDataBase = "Data Source";
protectedconststring CON_strUser = "UID";
protectedconststring CON_strPwd = "PWD";
protectedconststring CON_strConnTimeOut = "Connect Timeout = 2";
private DBType m_eDBType = DBType.Access;

protected DBAccess(DBType type)
...{
this.m_eDBType = type;
           }

public DBType DBType
...{
get...{ returnthis.m_eDBType; }
           }

publicvoid Init(string strServer, string strDataBase, string strUser, string strPwd)
...{
this.InitConn(strServer, strDataBase, strUser, strPwd);
           }

publicvoid Open()
...{
if (this.m_oConn != null)
...{
this.m_oConn.Open();
               }
           }

publicint RunNoQuery(string strCmd)
...{
int iRet = 0;
try
...{
                   DbCommand oCmd = this.GetCmd(strCmd);
if (oCmd != null)
...{
                       iRet = oCmd.ExecuteNonQuery();
                   }
               }
catch (Exception ex)
...{
throw (new Exception(ex.Message));
               }
return iRet;
           }

publicint GetFiledMax(string strTable, string strField)
...{
int iRet = -1;
               DataTable dt = this.RunQuery("Select Max(" + strField + ") From " + strTable);
if (dt != null && dt.Rows.Count == 1)
...{
                   iRet = dt.Rows[0][0] is DBNull ? 0 : Convert.ToInt32(dt.Rows[0][0]);
               }
return iRet;
           }

public DataTable RunQuery(string strCmd)
...{
               DataTable dt = new DataTable();
               DbDataAdapter adp = this.DbAdp;
               adp.SelectCommand = this.GetCmd(strCmd);
               adp.Fill(dt);
return dt;
           }

publicvoid Close()
...{
if (this.m_oConn != null && this.m_oConn.State == System.Data.ConnectionState.Open)
...{
this.m_oConn.Close();
               }
           }

publicbool TestConn()
...{
bool bRet = true;
try
...{
if (this.m_oConn.State != System.Data.ConnectionState.Open)
...{
this.m_oConn.Open();
                   }
                   bRet = this.m_oConn.State == System.Data.ConnectionState.Open;
               }
catch
...{
                   bRet = false;
               }
this.Close();
return bRet;
           }

publicabstract DataTable Tables ...{ get; }
publicabstract DataTable GetColumns();
publicabstract DataTable GetColumns(string strTable);

protectedabstractvoid InitConn(string strServer, string strDataBase, string strUser, string strPwd);
protectedabstract DbCommand GetCmd(string strCmd);
protectedabstract DbDataAdapter DbAdp ...{ get;}
       }

Access, SQL#region Access, SQL

privateclass Access : DBAccess
...{
public Access(DBType type)
               : base(type)
...{
           }

protectedoverridevoid InitConn(string strServer, string strDataBase, string strUser, string strPwd)
...{
string strConn = "Provider = ";
switch (strDataBase.Substring(strDataBase.LastIndexOf('.') + 1).ToLower())
...{
case "mdb":     // 2000, 2003
                       strConn += "Microsoft.Jet.OleDb.4.0;";
break;

case "accdb":   // 2007
                       strConn += "Microsoft.ACE.OLEDB.12.0;";
break;

default:
throw (new Exception("Unknown Access Version."));
//break;
               }
               strConn += CON_strDataBase + " = " + strDataBase;
//strConn += CON_strUser + " = " + strUser;
               //strConn += CON_strPwd + " = " + strPwd;
base.m_oConn = new OleDbConnection(strConn);
           }

protectedoverride DbCommand GetCmd(string strCmd)
...{
returnnew OleDbCommand(strCmd, (OleDbConnection)base.m_oConn);
           }

protectedoverride DbDataAdapter DbAdp
...{
get...{ returnnew OleDbDataAdapter(); }
           }

publicoverride DataTable Tables
...{
get
...{
return ((OleDbConnection)base.m_oConn).GetOleDbSchemaTable(OleDbSchemaGuid.Tables, newobject[] ...{ null, null, null, "Table" });
               }
           }

publicoverride DataTable GetColumns()
...{
               DataTable dt = new DataTable();
foreach (DataRow row inthis.Tables.Rows)
...{
                   dt.Merge(this.GetColumns(row["TABLE_NAME"].ToString()));
               }
return dt;
           }

publicoverride DataTable GetColumns(string strTable)
...{
return ((OleDbConnection)base.m_oConn).GetOleDbSchemaTable(OleDbSchemaGuid.Columns, newobject[] ...{ null, null, strTable, null });
           }
       }

privateclass SQL : DBAccess
...{
public SQL(DBType type)
               : base(type)
...{
           }

protectedoverridevoid InitConn(string strServer, string strDataBase, string strUser, string strPwd)
...{
string strConn = CON_strServer + " = " + strServer + ";";
               strConn += CON_strDataBase + " = " + strDataBase + ";";
               strConn += CON_strUser + " = " + strUser + ";";
               strConn += CON_strPwd + " = " + strPwd + ";";
               strConn += CON_strConnTimeOut;
base.m_oConn = new SqlConnection(strConn);
           }

protectedoverride DbCommand GetCmd(string strCmd)
...{
returnnew SqlCommand(strCmd, (SqlConnection)base.m_oConn);
           }

protectedoverride DbDataAdapter DbAdp
...{
get...{ returnnew SqlDataAdapter(); }
           }

publicoverride DataTable Tables
...{
get...{ return ((SqlConnection)base.m_oConn).GetSchema("Tables", null); }
           }

publicoverride DataTable GetColumns()
...{
return ((SqlConnection)base.m_oConn).GetSchema("Columns", null);
           }

publicoverride DataTable GetColumns(string strTable)
...{
return ((SqlConnection)base.m_oConn).GetSchema("Columns", newstring[] ...{ null, null, strTable, null });
           }
       }

#endregion
   }