c#数据库连接

//此方法是使用Windows身份验证连接本地sql数据库
using System;
using System.Data;
using System.Data.SqlClient;//连接sql数据库，需自己添加
using System.Windows.Forms;
namespace DataSearching
{
    public partial class Form1 : Form
    {
        private string ConnectionString ="Server = .;database=MyDatabase;integrated security = sspi";
        private SqlConnection conn = null;
        private SqlDataAdapter DataAdapter = null;
        private DataSet dataset = null;
        private SqlCommand cmd = null;
        public Form1()
        {
            InitializeComponent();
        }
        private void button1_Click(object sender, EventArgs e)
        {
            string tb1 = textBox1.Text;
            if (comboBox2.Text == " like ") tb1 = "%" + textBox1.Text + "%";
            string strSQL = "SELECT * FROM student Where ";
            strSQL += comboBox1.Text + comboBox2.Text + "'" + tb1 + "'";
            try
            {
                cmd.CommandText = strSQL;
                DataAdapter.SelectCommand = cmd;
                dataset.Clear();
                DataAdapter.Fill(dataset, "t1");
                dataGridView1.DataSource = dataset;
                dataGridView1.DataMember = "t1";
            }
            catch
            {
                MessageBox.Show("请正确设置检索条件！");
            }
            finally
            {
                if (conn != null) conn.Close();
            }
        }
        private void Form1_Load(object sender, EventArgs e)
        {
            try
            {
                conn = new SqlConnection(ConnectionString);
                conn.Open();
                DataAdapter = new SqlDataAdapter();
                dataset = new DataSet();
                cmd = new SqlCommand();
                cmd.Connection = conn;
                cmd.CommandText = "SELECT * FROM student";
                DataAdapter.SelectCommand = cmd;
                DataAdapter.Fill(dataset, "t1");
                comboBox1.Items.Clear();
                //先获取所有的字段，以用于构造查询条件
                for (int i = 0; i < dataset.Tables["t1"].Columns.Count; i++)
                    comboBox1.Items.Add(dataset.Tables["t1"].Columns[i].ToString());
                dataset.Clear();
                comboBox2.Items.Add(" = ");  //设置比较运算符
                comboBox2.Items.Add(" < ");
                comboBox2.Items.Add(" > ");
                comboBox2.Items.Add(" like ");
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }
    }
}

要连接Oracle数据库，需先添加OracleClient引用，然后引用System.Data.OracleClient命名空间，在使用OracleConnection对象进行连接。

注意：在使用VS时会找不到System.Data.OracleClient这个引用，可以使用以下方法解决；右击项目的属性，

在弹出窗口中有一个【目标框架】下拉框选项，默认全是，.Net FRAMWORK 4 CLIENT PROFILE(NET Framwork 4 Client profile 是 .NET Framework 4 简精版 )，

将此选项更改为 .NET FRAMEWORK 4。再打开【解决方法资源管理器】窗口，在项目的【引用】上单击鼠标右键，在弹出的快捷菜单中选择【添加引用】命令，添加OracleClient引用，就ok了

using System;
using System.Data;
using System.Data.OracleClient;
using System.Windows.Forms;
namespace DataSearching
{
    public partial class Form1 : Form
    {
        private string ConnectionString = "User Id = sunc; Password = hr;Data Source = xe";
        private OracleConnection conn = null;
        private OracleDataAdapter DataAdapter = null;
        private DataSet dataset = null;
        private OracleCommand cmd = null;
        public Form1()
        {
            InitializeComponent();
        }
        private void button1_Click(object sender, EventArgs e)
        {
            string tb1 = textBox1.Text;
            if (comboBox2.Text == " like ") tb1 = "%" + textBox1.Text + "%";
            string strSQL = "SELECT * FROM student Where ";
            strSQL += comboBox1.Text + comboBox2.Text + "'" + tb1 + "'";
            try
            {
                cmd.CommandText = strSQL;
                DataAdapter.SelectCommand = cmd;
                dataset.Clear();
                DataAdapter.Fill(dataset, "t1");
                dataGridView1.DataSource = dataset;
                dataGridView1.DataMember = "t1";
            }
            catch
            {
                MessageBox.Show("请正确设置检索条件！");
            }
            finally
            {
                if (conn != null) conn.Close();
            }
        }
        private void Form1_Load(object sender, EventArgs e)
        {
            try
            {
                conn = new OracleConnection(ConnectionString);
                conn.Open();
                DataAdapter = new OracleDataAdapter();
                dataset = new DataSet();
                cmd = new OracleCommand();
                cmd.Connection = conn;
                cmd.CommandText = "SELECT * FROM student";
                DataAdapter.SelectCommand = cmd;
                DataAdapter.Fill(dataset, "t1");
                comboBox1.Items.Clear();
                //先获取所有的字段，以用于构造查询条件
                for (int i = 0; i < dataset.Tables["t1"].Columns.Count; i++)
                    comboBox1.Items.Add(dataset.Tables["t1"].Columns[i].ToString());
                dataset.Clear();
                comboBox2.Items.Add(" = ");  //设置比较运算符
                comboBox2.Items.Add(" < ");
                comboBox2.Items.Add(" > ");
                comboBox2.Items.Add(" like ");
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }
    }
}

其中 private string ConnectionString = "User Id = sunc; Password = hr;Data Source = xe";
User Id 为用户名，password 为用户名对应的密码；
Data Sourse 获取方式：打开数据库，连接上用户，右击用户名查看属性 对应SID内容即为DATA SOURCE；