例子一，获取三小时前的记录
public static DataTable Query()
{
const string sSql = "select xh,lsh,name from table where gxsj>to_date(:gxsj,'yyyy-MM-dd HH24:mi:ss')";
OracleParameter[] parameters = {new OracleParameter(":gxsj", OracleType.VarChar, 10)};
parameters[0].Value = DateTime.Now.AddHours(-3).ToStrin
