var query = User.GroupJoin(Charge, u => u.Account, c => c.Account, (u, c) => new { u, c })
.Select(data => new AnalysisPlayer { Account = data.u.Account, PlayerName = data.u.Name, 
RegTime = data.u.CreateTime ?? DateTime.Now, Points = 此处如何写代码 });

public class AnalysisPlayer
{
        /// <summary>
        /// 玩家名称
        /// </summary>
        public string PlayerName { get; set; }
        /// <summary>
        /// 玩家账号
        /// </summary>
        public string Account { get; set; }
        /// <summary>
        /// 注册时间
        /// </summary>
        public DateTime RegTime { get; set; }
        /// <summary>
        /// 充值总数
        /// </summary>
        public int Points { get; set; }
}