c#中executereader执行查询实例

ExecuteReader执行查询实例
ExecuteReader方法存在的目的只有一个：尽可能快地对数据库进行查询并得到结果。ExecuteReader 返回一个DataReader对象：如果在SqlCommand对象中调用，则返回SqlDataReader；如果在OleDbCommand对象中调用，返回的是OleDbDataReader。可以调用DataReader的方法和属性迭代处理结果集。它是一个快速枚举数据库查询结果的机制，是只读、只进的。对SqlDataReader.Read的每次调用都会从结果集中返回一行。
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.Data.SqlClient;
namespace ExecuteReader执行查询
{
///

/// Window1.xaml 的交互逻辑
///

public partial class Window1 : Window
{
public Window1()
{
InitializeComponent();
}
private void button1_Click(object sender, RoutedEventArgs e)
{
using (SqlConnection conn = new SqlConnection("Data Source=.;Initial Catalog=MyTest;User Id=sa;Password=123;"))
{
conn.Open();
using (SqlCommand cmd = conn.CreateCommand())
{
cmd.CommandText = "select * from T_Student where Age<100";
using (SqlDataReader reader = cmd.ExecuteReader())//ExecuteReader返回的对象类型是SqlDataReader
{
//Read是bool类型，初始指针指向第一条数据之前，每调用一次reader，指针就下移一条，只要没有移到最后一条之后，就返回true。
while (reader.Read())
{
string name = reader.GetString(1);//GetString(1)得到表中第一列的值，用name接收，因为查的是*，所以就和表中的列数一样。
int age = reader.GetInt32(2);
MessageBox.Show(name+","+age);
}
}
}
}
}
private void btnQuery_Click(object sender, RoutedEventArgs e)
{
using (SqlConnection conn = new SqlConnection("Data Source=.;Initial Catalog=MyTest;User Id=sa;Password=123;"))
{
conn.Open();
using (SqlCommand cmd = conn.CreateCommand())
{
//cmd.CommandText = "select age from T_Student where name='"+ txtName.Text +"'";//字符串拼接查找数据库。
cmd.CommandText = "select age from T_Student where name=@name or age>@age";//与数据库进行数据对比。
//@参数:不能用来替换表名，字段名，select之类的关键字等。
cmd.Parameters.Add(new SqlParameter("@name",txtName.Text));
cmd.Parameters.Add(new SqlParameter("@age",Convert.ToInt32(txtAge.Text)));
using (SqlDataReader reader = cmd.ExecuteReader())
{
while (reader.Read())
{
//GetInt32获得的是int类型
//GetInt64获得的是long类型（bigint）
int age = reader.GetInt32(0);//GetInt32(0)中的参数是看cmd.CommandText中的查询结果有几个。
MessageBox.Show(age.ToString());
}
}
}
}
}
private void btnHobby_Click(object sender, RoutedEventArgs e)
{
using (SqlConnection conn = new SqlConnection("Data Source=.;Initial Catalog=MyTest;User Id=sa;Password=123;"))
{
conn.Open();
using (SqlCommand cmd = conn.CreateCommand())
{
cmd.CommandText = "select * from T_Student where name like '张%'";
using (SqlDataReader reader = cmd.ExecuteReader())
{
while (reader.Read())
{
string hobby = reader.GetString(3);
MessageBox.Show(hobby);
}
}
}
}
}
private void btnQuery1_Click(object sender, RoutedEventArgs e)
{
using (SqlConnection conn = new SqlConnection("Data Source=.;Initial Catalog=MyTest;User Id=sa;Password=123;"))
{
conn.Open();
using (SqlCommand cmd = conn.CreateCommand())
{
cmd.CommandText = "select hobbit from T_Student where age>@age or hobbit =@hobbit";
cmd.Parameters.Add(new SqlParameter("@age", txtAge1.Text));
cmd.Parameters.Add(new SqlParameter("@hobbit",txtHobby.Text));
using (SqlDataReader reader = cmd.ExecuteReader())
{
while (reader.Read())
{
string str = reader.GetString(0);
MessageBox.Show(str);
}
}
}
}
}
}
}