ADO.NET操纵数据库

SqlCommand cmd;     
string 
strCon="server=localhost;database=Northwind;Trusted_Connection=Yes;";
string strqry="select * from Categories";
SqlConnection con=new SqlConnection(strCon);
con.Open();
1cmd=con.CreateCommand(); //这里使用用Connection对象的
CreateCommand方法来创建一个Command对象。
cmd.CommandText=strqry;
// SqlDataReader reader=cmd.ExecuteReader();
2cmd=new SqlCommand(); //直接使用new 关键字来创建
cmd.CommandText=strqry;
cmd.Connection=con; //设置与数据库的连接

3cmd=new SqlCommand(strqry,con);　//直接在new的时候带两个参数来创建

int id=reader.GetOrdinal("CategoryName");
while(reader.Read())
{
Response.Write(reader[id]);
}
reader.Close();

while(reader.Read())
{
Response.Write(reader.GetInt32(0).ToString()+" "
+reader.GetString(1).ToString()+" 
");
}

int affectrows=cmd.ExecuteNonQuery();
Response.Write(affectrows +" 条记录受影响");

string strCon="server=localhost;database=Northwind;Trusted_Connection=Yes;";
string strqry="select count(*) from Categories";
SqlConnection con=new SqlConnection(strCon);
con.Open();
SqlCommand cmd=con.CreateCommand();
int i=Convert.ToInt32(cmd.ExecuteScalar());　//必须强制转换

string strCon="server=localhost;database=Northwind;Trusted_Connection=Yes;";
SqlConnection con=new SqlConnection(strCon);
con.Open();
SqlCommand cmd = new SqlCommand("select * 
from Categories FOR XML AUTO, XMLDATA", con);
XmlReader xr=cmd.ExecuteXmlReader();
Response.Write(xr.AttributeCount);//这里获取当前节点上的属性个数 
xr.Close();

string strCon="server=localhost;database=Northwind;Trusted_Connection=Yes;";
SqlConnection con=new SqlConnection(strCon);
con.Open();
string strqry="select * from Categories where CategoryID=@CategoryID";　//带参数的查询
SqlCommand cmd=new SqlCommand(strqry,con);
cmd.Parameters.Add("@CategoryID",SqlDbType.Int,4);　//给参数赋于同数据库中相同的类型
cmd.Parameters["@CategoryID"].Value="3";　//给参数赋值，可灵活改变
SqlDataReader r=cmd.ExecuteReader();　
while(r.Read())
{
Response.Write(r.GetString(2)+"
");　//取出指定参数列的值
}
con.Close();　//切记关闭