使用ADO.NET查询和操作数据

StringBuilder类： 用来定义可变字符串
StringBuilder sb = new StringBuilder("");
//追加字符串
sb.Append("World");
sb.Append("!");
//W2orld
sb.Insert(2, "2");
//原字符串：Wo2rld! 截取之后：W2rld!
sb.Remove(1, 2);
//ToString()
Console.WriteLine(sb.ToString());

查询学生记录数
//打开数据库连接
con.Open();
//使用StringBuilder追加SQL语句
StringBuilder sb = new StringBuilder();
sb.Append("select ");
sb.Append(" Count(*) ");
sb.Append(" from ");
sb.Append("[Student]");
Console.WriteLine(sb.ToString());
//创建一个SqlCommand对象
SqlCommand com = new SqlCommand(sb.ToString(),con);
Console.WriteLine((int)com.ExecuteScalar());

DataReader：从数据源中检索只读、只进的数据流，每次读取一行数据

StringBuilder sb = new StringBuilder();
sb.AppendLine("select");
sb.AppendLine("[StudentNo]");
sb.AppendLine(",[StudentName]");
sb.AppendLine("from");
sb.AppendLine("[Student]");
SqlCommand com = new SqlCommand(sb.ToString(), con);
//从数据源中检索只读、只进的数据流
return com.ExecuteReader();

SqlDataReader reader=GetStudentInfo();
while (reader.Read())
{
Console.WriteLine("{0} {1}",reader["StudentNo"],reader["StudentName"]);
}
reader.Close();

ExecuteNonQuery():

StringBuilder sb = new StringBuilder();
sb.AppendLine("Insert into");
sb.AppendLine("[Grade]([GradeName])");
sb.AppendLine("Values('" + gradeName + "')");
//3.创建一个SqlCommand
SqlCommand com = new SqlCommand(sb.ToString(),con);
//4.返回执行结果
return com.ExecuteNonQuery();

Student stu = new Student();
Console.WriteLine("请输入年级名称：");
string gradename = Console.ReadLine();
int count = stu.AddGrade(gradename);
if (count > 0)
{
Console.WriteLine("success！");
}
else
{
Console.WriteLine("success mother!");
}

class Test
    {
        string connString = "Data Source = .;Initial Catalog= Library;User Id = Sa;Pwd = asiga0.";
        //判断用户
        public bool CheckUser(string UserId, string Password) {
            String s = "select count(*) from user1 where loginid='" + UserId + "'and loginpwd = '" + Password + "'";//空格错误!
            SqlConnection conn = new SqlConnection(connString);
            SqlCommand comm = new SqlCommand(s, conn);
            try
            {
                conn.Open();
                if ((int)comm.ExecuteScalar()>0
                    )
                {
                    Console.WriteLine("登陆成功");
                    return true;
                }
                else
                {
                    Console.WriteLine("登录失败");
                    return false;
                }
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
                return false;
            }
            finally
            {
                conn.Close();
            }
        }

        //主菜单
        public void List() {
            do
            {
                Console.WriteLine("====请选择操作键====");
                Console.WriteLine("1.查看全部图书");
                Console.WriteLine("2.插入图书信息");
                Console.WriteLine("3.修改图书信息");
                Console.WriteLine("4.删除图书信息");
                Console.WriteLine("5.退出");
                Console.WriteLine("===============");
                int i = int.Parse(Console.ReadLine());
                switch (i)
                {
                    case 1:
                        One();
                        break;
                    case 2:
                        Two();
                        break;
                    case 3:
                        Three();
                        break;
                    case 4:
                        Four();
                        break;
                    case 5:
                        Console.WriteLine("谢谢使用,再见!");
                        return;
                    default:
                        break;
                }
                Console.WriteLine("继续吗?(Y/N)");
                if (!Console.ReadLine().ToLower().Trim().Equals("y"))
                {
                    break;
                }
            } while (true);
        }
        public void One() {
            SqlConnection conn = new SqlConnection(connString);
          
            try
            {  
                String s = "select book.id,book.name,booktype.typename,book.number,book.price from book,booktype where book.typle=booktype.typle";
                Console.WriteLine("------------------------------------------------");
                Console.WriteLine("编号	名称		类别	数量	价格");
                Console.WriteLine("------------------------------------------------");
                SqlCommand comm = new SqlCommand(s, conn);
                conn.Open();
                SqlDataReader rd = comm.ExecuteReader();
                while (rd.Read())
                {
                    Console.WriteLine("{0}	{1}	{2}	{3}	{4}", rd["id"], rd["name"], rd["typename"], rd["number"], rd["price"]);//前面不能加" . "
                }
                rd.Close();
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);

            }
            finally
            {
                conn.Close();
            }
        }
        public void Two() {
                SqlConnection conn = new SqlConnection(connString);
                try
                {
                    Console.WriteLine("请输入图书编号");
                    int Id = int.Parse(Console.ReadLine());
                    if (GetBookByID(Id))
                    {
                        Console.WriteLine("图书记录已存在,请重新输入!");
                        return;
                    }
                    Console.WriteLine("请输入图书名称");
                    string name = Console.ReadLine();
                    Console.WriteLine("请插入图书类型编号");
                    int type = int.Parse(Console.ReadLine());
                    if (GetBookTypeByID(type)) { }
                    else { Console.WriteLine("不存在,请重新输入"); return; }
                    Console.WriteLine("请插入图书数量");
                    int number = int.Parse(Console.ReadLine());
                    Console.WriteLine("请输入图书单价");
                    float price = float.Parse(Console.ReadLine());
                    String s = string.Format("insert book(id,name,typle,number,price) values({0},'{1}',{2},{3},{4})", Id, name, type, number, price);
                    SqlCommand comm = new SqlCommand(s, conn);
                    conn.Open();//忘记开启
                    if (comm.ExecuteNonQuery() > 0)
                    {
                        Console.WriteLine("插入成功!");
                    }
                    else
                    {
                        Console.WriteLine("插入失败");
                    }
                }
                catch (Exception ex)
                {
                    Console.WriteLine(ex.Message);
                }
                finally
                {
                    conn.Close();
                }
        }
        public bool GetBookByID(int bookId) {
                SqlConnection conn = new SqlConnection(connString);
                string s = "select id from book where id=" + bookId;
                SqlCommand comm = new SqlCommand(s, conn);
                conn.Open();
                SqlDataReader rd = comm.ExecuteReader();
                try
                {
                    if (rd.Read())
                    {
                        return true;
                    }
                    else
                    {
                        return false;
                    }
                }
                catch (Exception ex)
                {
                    Console.WriteLine(ex.Message);
                    return true;
                }
                finally
                {
                    rd.Close();
                    conn.Close();
                }
        }
        public bool GetBookTypeByID(int typeId) {
            SqlConnection conn = new SqlConnection(connString);
            string s = "select typle,typename from booktype where typle=" + typeId;
            SqlCommand comm = new SqlCommand(s, conn);
            conn.Open();
            SqlDataReader rd = comm.ExecuteReader();
            try
            {
                if (rd.Read())
                {
                    Console.WriteLine("{0}	{1}", rd["typle"], rd["typename"]);
                    return true;
                }
                else
                {
                    return false;
                }
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
                return false;
            }
            finally
            {
                rd.Close();
                conn.Close();
            }
        }
        public void Three() {
            Console.WriteLine("请输入图书编号");
            int id = int.Parse(Console.ReadLine());
            if (GetBookByID(id))
            {
                Console.WriteLine("请输入修改后的价格($.00):");
                float f = float.Parse(Console.ReadLine());
                if (ChangePrice(id, f) > 0)
                {
                    Console.WriteLine("修改成功");
                }
                else
                {
                    Console.WriteLine("修改失败");
                }
            }
            else
            {
                Console.WriteLine("不存在该编号,请重新输入");
                return;
            }   
        }
        public int ChangePrice(int id,float price) {
            SqlConnection conn = new SqlConnection(connString);
            try
            {
                String s = string.Format("update book set price ={0} where id={1}", price, id);
                SqlCommand comm = new SqlCommand(s, conn);
                conn.Open();
                return comm.ExecuteNonQuery();
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
                return -1;
            }
            finally
            {
                conn.Close();
            }
        }
        public void Four() {
            Console.WriteLine("请输入图书编号");
            int id = int.Parse(Console.ReadLine());
            if (GetBookByID(id))
            {
                show(id);
                Console.WriteLine("将删除该图书记录,确认吗?(Y/N)");
                if (Console.ReadLine().ToLower().Trim().Equals("y")) {
                    if (DeleteBookByID(id) > 0)
                    {
                        Console.WriteLine("修改成功");
                    }
                    else
                    {
                        Console.WriteLine("修改失败");
                    }
                }
                else 
                {
                    Console.WriteLine("未删除,返回"); 
                }
            }
            else
            {
                Console.WriteLine("编号不存在,重新输入");
                return;
            }
        }
        public void show(int id) {
            SqlConnection conn = new SqlConnection(connString);
            try
            {
                String s = "select book.id,book.name,booktype.typename,book.number,book.price from book,booktype where book.typle=booktype.typle and book.id="+id;
                Console.WriteLine("------------------------------------------------");
                Console.WriteLine("编号	名称		类别	数量	价格");
                Console.WriteLine("------------------------------------------------");
                SqlCommand comm = new SqlCommand(s, conn);
                conn.Open();
                SqlDataReader rd = comm.ExecuteReader();
                while (rd.Read())
                {
                    Console.WriteLine("{0}	{1}	{2}	{3}	{4}", rd["id"], rd["name"], rd["typename"], rd["number"], rd["price"]);//前面不能加" . "
                }
                rd.Close();
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);

            }
            finally
            {
                conn.Close();
            }
        }
        public int DeleteBookByID(int id) {
            SqlConnection conn = new SqlConnection(connString);
            String s = "Delete from book where id=" + id;
            SqlCommand comm = new SqlCommand(s, conn);
            try
            {
                conn.Open();
                return comm.ExecuteNonQuery();
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
                return -1;
            }
            finally
            {
                conn.Close();
            }
        }
    }