使用ADO.NET查询和操作数据库

String和StringBuilder

语法：

//声明一个空的StringBuilder对象

StingBuilder对象名称 = new   StringBuilder();

//声明一个StringBuilder对象，值为"字符串初始值"

StringBuilder  对象名称 = new  StringBuilder("字符串的初始值");

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}\t{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!");

}