C# SQL查询代码

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class SqlDbHelper    {        private static SqlConnection conn;        private static string mConnectionString;        private SqlDbHelper(){}        /// <summary>        /// 判断数据库服务器是否存在        /// </summary>        /// <returns> true:存在</br> false:不存在</returns>        public static bool open(string connectionString)        {            mConnectionString = connectionString;            conn = new SqlConnection(connectionString);                        try            {                conn.Open();            }            catch (Exception)            {                return false;            }                        return true;                    }        public static bool isAlive()        {            bool ret = false;            try            {                close();                ret = open(mConnectionString);            }            catch (Exception)            {                ret = false;            }            return ret;        }        /// <summary>        /// 关闭        /// </summary>        public static void close()        {            if (conn != null)            {                if (conn.State == ConnectionState.Open)                {                    conn.Close();                    conn.Dispose();                }                conn = null;            }        }        /// <summary>        /// 根据参数查询数据库表内容        /// </summary>        /// <param name="cmdText">SQL 语句</param>        /// <param name="values">查询参数</param>        /// <returns>查询表结果DataTable</returns>        public static DataTable executeNonQuery(string cmdText, SqlParameter[] values)        {            try            {                using (SqlCommand cmd = conn.CreateCommand())                {                    cmd.CommandText = cmdText;                    if (values == null)                    {                        cmd.Parameters.AddRange(new SqlParameter[] { });                    }                    else                    {                        cmd.Parameters.AddRange(values);                    }                                            SqlDataAdapter sd = new SqlDataAdapter(cmd);                    DataTable dt = new DataTable();                    sd.Fill(dt);                                         return dt;                }            }            catch (Exception)            {                return null;            }        }    }
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