ADO.net公共增删改查

public class DBhelper
    {
        public static SqlConnection conn = new SqlConnection("Data Source=.;Initial Catalog=库名;User ID=密码");

        //查询
        public SqlDataReader select(string sql)
        {
            SqlDataReader reader = null;
            conn.Open();
            SqlCommand comm = new SqlCommand(sql, conn);
            reader = comm.ExecuteReader(System.Data.CommandBehavior.CloseConnection);
            return reader;
        }
        //删除、添加、更改
        public static int ExecuteUpdate(string sql)
        {
            int result = 0;
            conn.Open();
            SqlCommand comm = new SqlCommand(sql, conn);
            result = comm.ExecuteNonQuery();
            conn.Close();
            return result;
        }
        //单条数据的查询
        public static Object ExecteOnlyOneVaule(string sql)
        {
            Object obj = null;
            conn.Open();
            SqlCommand comm = new SqlCommand(sql, conn);
            obj = comm.ExecuteScalar();
            conn.Close();
            return obj;
        }
    }