C# ADO.NET参数查询

 1 using System;
 2 using System.Collections.Generic;
 3 using System.ComponentModel;
 4 using System.Data;
 5 using System.Data.SqlClient;
 6 using System.Drawing;
 7 using System.Text;
 8 using System.Windows.Forms;
 9 
10 namespace AdoTwo
11 {
12     public partial class FLogin : Form
13     {
14         public FLogin()
15         {
16             InitializeComponent();
17         }
18 
19         private void btnOk_Click(object sender, EventArgs e)
20         {
21             string tname = txtName.Text.Trim();//a
22             string tpwd = txtPwd.Text.Trim();//b
23             //判断用户名密码是否正确其实就是去数据库查询有没有一条数据，
24             //这条数据是用户名等于用户输入的用户名,
25             //并且
26             //密码等于用户输入的密码的一条数据
27             SqlConnection conn = new SqlConnection("server=.;database=heimablog;uid=sa;pwd=suncoder");
28             string sql=string.Format("select count(id) from Student where Name=‘{0}‘ and Pwd=‘{1}‘",tname,tpwd);
29             SqlCommand cmd = new SqlCommand(sql, conn);
30             //cmd.Connection = conn;
31             //cmd.CommandText = "";
32             conn.Open();
33 
34             //SqlDataReader dr = cmd.ExecuteReader();
35             //if (dr.HasRows) 
36             //{
37             //    MessageBox.Show("登陆成功");
38             //}
39             //while (dr.Read())
40             //{
41             //    Console.WriteLine(dr[1].ToString());//+dr["Name"],dr.GetString(1));
42             //}
43 
44             object obg = cmd.ExecuteScalar();
45             int res = Convert.ToInt32(obg);
46             if (res > 0) { MessageBox.Show("登陆成功"); }
47             else { MessageBox.Show("登陆失败"); }
48         }
49 
50         private void btnLoginPara_Click(object sender, EventArgs e)
51         {
52             SqlConnection conn = new SqlConnection("server=.;database=heimablog;uid=sa;pwd=suncoder");
53             SqlCommand cmd = new SqlCommand("select count(id) from Student where Name=@ass and Pwd=@add", conn);
54 
55             //第一种写法
56             //SqlParameter sp = new SqlParameter("@ass", txtName.Text.Trim());
57             //SqlParameter sp2 = new SqlParameter("@add", txtPwd.Text.Trim());
58 
59             //cmd.Parameters.Add(sp);
60             //cmd.Parameters.Add(sp2);
61 
62             //第二种写法，特殊情况下报错
63             //cmd.Parameters.Add(new SqlParameter("@ass", txtName.Text.Trim()));
64             //cmd.Parameters.Add(new SqlParameter("@add", txtPwd.Text.Trim()));
65 
66             //第三种写法
67             //SqlParameter[] spa = new SqlParameter[]{
68             //    new SqlParameter("@ass", txtName.Text.Trim()),
69             //    new SqlParameter("@add", txtPwd.Text.Trim())
70             //};
71             //cmd.Parameters.AddRange(spa);
72 
73             //第四种写法
74             //cmd.Parameters.AddWithValue("@ass", txtName.Text.Trim());
75             //cmd.Parameters.AddWithValue("@add", txtPwd.Text.Trim());
76 
77             //第五种写法,参数可以为输出参数
78             //SqlParameter sp = new SqlParameter("@ass", SqlDbType.NVarChar);
79             //SqlParameter sp2 = new SqlParameter("@add", SqlDbType.Char);
80             //sp.Value = txtName.Text.Trim();
81             //sp2.Value = txtPwd.Text.Trim();
82             //cmd.Parameters.Add(sp);
83             //cmd.Parameters.Add(sp2);
84 
85             //第六种写法
86             SqlParameter sp = new SqlParameter("@ass", SqlDbType.NVarChar) { Value = txtName.Text.Trim() };
87             SqlParameter sp2 = new SqlParameter("@add", SqlDbType.Char) { Value = txtPwd.Text.Trim() };
88             cmd.Parameters.Add(sp);
89             cmd.Parameters.Add(sp2);
90 
91             conn.Open();
92 
93             MessageBox.Show(cmd.ExecuteScalar().ToString());
94 
95         }
96     }
97 }