在 .net 中处理数据库异常

try
{
    // 执行数据库操作
}
catch (SqlException ex)
{
    // 处理数据库异常
}

using (SqlConnection connection = new SqlConnection(connectionString))
{
    connection.Open();

    SqlTransaction transaction = connection.BeginTransaction();

    try
    {
        // 执行数据库操作

        transaction.Commit();
    }
    catch (SqlException ex)
    {
        transaction.Rollback();

        // 处理数据库异常
    }
}

using (SqlConnection connection = new SqlConnection(connectionString))
{
    connection.Open();

    // 执行数据库操作
}

using (SqlConnection connection = new SqlConnection(connectionString))
{
    connection.Open();

    using (SqlCommand command = new SqlCommand("SELECT * FROM Users WHERE Username = @Username AND Password = @Password", connection))
    {
        command.Parameters.AddWithValue("@Username", username);
        command.Parameters.AddWithValue("@Password", password);

        using (SqlDataReader reader = command.ExecuteReader())
        {
            // 读取查询结果
        }
    }
}