C# 跟查询有关的代码

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Data.SqlClient;

namespace hetaoTest
{
    public partial class Form1 : Form
    {
       static SqlConnection conn = null;
        public Form1()
        {
            InitializeComponent();
        }

        private void textBox1_TextChanged(object sender, EventArgs e)
        {

        }
        /// <summary>
        /// 添加的方法
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void button1_Click(object sender, EventArgs e)
        {
            try
            {

                {
                string conStr = "Data Source=127.0.0.1;Initial Catalog=TestDB;Integrated Security=True";
                conn = new SqlConnection(conStr);
                conn.Open();
                SqlCommand cmd = conn.CreateCommand();
                //-----------------------------添加方法1-----------------------------
                //cmd.CommandText = "insert into T_UserName(name,age)Values('" + txtName.Text.Trim() + "','" 
                 //   + txtAge.Text.Trim() + "')";
                //-----------------------------添加方法2-----------------------------
                cmd.CommandText = "INSERT INTO T_UserName(name,age)VALUES(@name,@age)";
                //cmd.Parameters.AddWithValue("@name",txtName.Text.Trim());
                //cmd.Parameters.AddWithValue("@age",txtAge.Text.Trim());
                //-----------------------------添加方法3-----------------------------
                cmd.Parameters.Add("@name", SqlDbType.VarChar);
                cmd.Parameters["@name"].Value = txtName.Text.Trim();

                cmd.Parameters.Add("@age", SqlDbType.VarChar);
                cmd.Parameters["@age"].Value = txtAge.Text.Trim();
                if (MessageBox.Show("确定添加么？", "My Application", MessageBoxButtons.YesNo, MessageBoxIcon.Question)
                     == DialogResult.Yes)
                {

                    cmd.ExecuteNonQuery();
                }


                
                }
            }
            catch(Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }

        /// <summary>
        /// 使用sqlcommand对象来返回数据集合的方法
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>

        private void Form1_Load(object sender, EventArgs e)
        {
            string connStr = "Data Source=127.0.0.1;Initial Catalog=TestDB;Integrated Security=True";
            string SqlStr = "SELECT * FROM T_UserName";
            SqlConnection conn = new SqlConnection(connStr);
            conn.Open();
            SqlCommand cmd = conn.CreateCommand();
            cmd.CommandText = SqlStr;

           //int flat = (int)(cmd.ExecuteScalar());
           //MessageBox.Show(Convert.ToString(flat));

            SqlDataAdapter adp = new SqlDataAdapter(cmd);
            DataTable dt = new DataTable();
            adp.Fill(dt);

            dataGridView1.DataSource = dt;


        }

        /// <summary>
        /// 
        ///使用sqlcommand对象来返回SQL执行正确与否
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>

        private void btnScan1_Click(object sender, EventArgs e)
        {
            string connStr = "Data Source=127.0.0.1;Initial Catalog=TestDB;Integrated Security=True";
            string sqlStr = "SELECT * FROM T_UserName1";
            SqlConnection conn = new SqlConnection(connStr);
            conn.Open();
            SqlCommand cmd = conn.CreateCommand();
            cmd.CommandText = sqlStr;
            try
            {
                cmd.ExecuteNonQuery();
                MessageBox.Show("成功查询", "提示", MessageBoxButtons.OKCancel, MessageBoxIcon.Question);
            }

            catch
            {
                MessageBox.Show("查询失败", "提示", MessageBoxButtons.OK, MessageBoxIcon.Question);
            }
        }

        private void button2_Click(object sender, EventArgs e)
        {
            Application.Exit();
        }



        /// <summary>
        ///   使用sqlcommand对象来操作存储过程
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void button4_Click(object sender, EventArgs e)
        {
            string strconn = "Data Source=127.0.0.1;Initial Catalog=TestDB;Integrated Security=True";
            SqlConnection conn = new SqlConnection(strconn);
            conn.Open();
            SqlCommand sqlcmd = new SqlCommand();
            sqlcmd.CommandText = "a";
            sqlcmd.CommandType = CommandType.StoredProcedure;
            sqlcmd.Connection = conn;
            //sqlcmd.Parameters.Add("@param1", textBox1.Text.Trim());
            //sqlcmd.Parameters.Add("@param2", textBox2.Text.Trim());
            //sqlcmd.Parameters.Add("@param3", textBox3.Text.Trim());

            SqlDataAdapter adp = new SqlDataAdapter(sqlcmd);
            DataTable dt = new DataTable();
            adp.Fill(dt);
            dataGridView1.DataSource = dt;
        }

        private void button3_Click(object sender, EventArgs e)
        {
            string connStr = "Data Source=127.0.0.1;Initial Catalog=TestDB;Integrated Security=True";
            string SqlStr = "SELECT * FROM T_UserName";
            SqlConnection conn = new SqlConnection(connStr);
            conn.Open();
            SqlCommand cmd =new SqlCommand(SqlStr,conn);

            SqlDataReader dr = cmd.ExecuteReader();//返回只能读取,不能写入的SqlDataReader对象

            while (dr.Read())
            {
                MessageBox.Show("ID："+dr.GetValue(0)+"   Name: "+dr.GetValue(1)+"   Age: "+dr.GetValue(2)+"  Sex: "+dr.GetValue(3));
            }


        }
        /// <summary>
        /// ExecuteNonQuery方法
        ///一般修改,删除,插入都用它
        ///返回受影响的行数。
        /// sql="update 表 set 栏位1=值1，栏位2=值2 where (条件);"
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void button5_Click(object sender, EventArgs e)
        {
            string connStr = "Data Source=127.0.0.1;Initial Catalog=TestDB;Integrated Security=True";
            string sqlStr = "Update T_UserName set name='Admin',Age='100',Sex='男' where(ID=66)";
            SqlConnection conn = new SqlConnection(connStr);
            conn.Open();
            SqlCommand cmd = new SqlCommand(sqlStr,conn);
            cmd.ExecuteNonQuery();
            MessageBox.Show("修改成功！");
        }
    }
}

ExecuteScalar方法

执行查询，并返回查询所返回的结果集中第一行的第一列。所有其他的列和行将被忽略。

using System;
using System.Data.SqlClient;
public class Lvcha
{
  public static void Main(string[] args)
  {
    string source="Server =192.168.1.100; User ID=ac_sy_guest; Password=guest1314; Initial CataLog=Account";
    string select="select count(*) from dbUser";
    SqlConnection conn=new SqlConnection(source);
    conn.Open();
    SqlCommand cmd=new SqlCommand(select,conn);
    object o=cmd.ExecuteScalar();
    Console.WriteLine(o);
    Console.ReadLine();
  }
}

ExecuteNonQuery用于执行不返回任何记录的SQL语句或存储过程。在数据库执行如更新、插入、删除操作时，应使用这个方法。ExecuteNonQuery返回一个整数值，用来说明受查询语句影响的行数。
connection.Open();
command.ExecuteNonQuery();
command.Close();   

ExecuteScalar与ExecuteNonQuery一样，其返回的也是单值，但该返回值是从数据库中读出来的，而不是受影响的行数。它通常用于选择一个值的SQL语句。如果SELECT返回多行或多列，则使用该方法仅返回第一行第一列的数据。

ExecuteReader被用于返回多条记录的SELECT语句（包含任意个字段）。ExecuteReader将返回一个包含查询结果的SqlDataReader对象。一个SqlDataReader对象是以顺序向前且只读的形式逐个读取并返回结果的。SqlDataReader是数据库中读取数据最快的对象，但必须打开连接。通过SqlDataReader取回所有的记录，并把它们存入DataTable对象中（它可以存储离线数据而不需要一个打开的连接），这样就可以马上关闭数据库连接了。DataTable类可以存放本地的结果集而不需要一个打开的SQL Server连接，和其它的ADO.NET对象一样，它也不是特定于某种数据提供程序的。

conn.Open();
SqlDataReader reader = comm.ExecuteReader();
DataTable table = new DataTable();
table.Load(reader);
reader.Close();
conn.Close();