下面是一个使用ADO.NET连接数据库并查询数据的简单案例：
```csharp
using System;
using System.Data;
using System.Data.SqlClient;
class Program
{
static void Main()
{
string connectionString = "Data Source=(localdb)\\MSSQLLocalDB;Initial Catalog=SampleDB;Integrated Security=True";
using (SqlConnection connection = new SqlConnection(connectionString))
{
connection.Open();
// 创建并执行 SQL 查询
string query = "SELECT * FROM Employees";
SqlCommand command = new SqlCommand(query, connection);
SqlDataReader reader = command.ExecuteReader();
// 读取查询结果
while (reader.Read())
{
int employeeId = (int)reader["EmployeeId"];
string firstName = (string)reader["FirstName"];
string lastName = (string)reader["LastName"];
Console.WriteLine("Employee ID: {0}, Name: {1} {2}", employeeId, firstName, lastName);
}
reader.Close();
}
}
}
```
