完成双色球系统，可以让用户输入想购买的号码，开奖功能并把每次中奖号码都写入数据库，查询以往三期中奖号码

好的，这是一个比较完整的系统，需要涉及到数据库的设计和编程实现。以下是一个简单的实现方案：

1. 数据库设计

首先需要设计数据库表，包括彩票购买记录表、彩票开奖记录表等。可以用MySQL或者SQLite等关系型数据库来实现。

购买记录表结构如下：

purchase_record
- id (int, primary key)
- user_id (int)
- ticket_number (varchar)
- purchase_time (datetime)

开奖记录表结构如下：

lottery_record
- id (int, primary key)
- lottery_number (varchar)
- lottery_time (datetime)

2. 实现购买功能

客户输入需要购买的号码后，将号码和购买时间插入到购买记录表中。可以用Python的Flask框架来实现Web应用，用SQLAlchemy来操作数据库。

代码示例：

from flask import Flask, request
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///lottery.db'
db = SQLAlchemy(app)

class PurchaseRecord(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    user_id = db.Column(db.Integer)
    ticket_number = db.Column(db.String(20))
    purchase_time = db.Column(db.DateTime)

@app.route('/buy', methods=['POST'])
def buy_lottery():
    user_id = request.form['user_id']
    ticket_number = request.form['ticket_number']
    purchase_time = datetime.now()
    record = PurchaseRecord(user_id=user_id, ticket_number=ticket_number, purchase_time=purchase_time)
    db.session.add(record)
    db.session.commit()
    return '购买成功'

if __name__ == '__main__':
    app.run()

3. 实现开奖功能

开奖需要生成随机的彩票号码，并将开奖记录插入到开奖记录表中。可以用Python的random模块来生成随机号码。开奖后需要遍历购买记录表，找出所有中奖的彩票，并将中奖记录插入到中奖记录表中。

代码示例：

from datetime import datetime
import random

from flask import Flask, request
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///lottery.db'
db = SQLAlchemy(app)

class PurchaseRecord(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    user_id = db.Column(db.Integer)
    ticket_number = db.Column(db.String(20))
    purchase_time = db.Column(db.DateTime)

class LotteryRecord(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    lottery_number = db.Column(db.String(20))
    lottery_time = db.Column(db.DateTime)

class WinningRecord(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    user_id = db.Column(db.Integer)
    ticket_number = db.Column(db.String(20))
    lottery_number = db.Column(db.String(20))
    winning_time = db.Column(db.DateTime)

@app.route('/draw', methods=['POST'])
def draw_lottery():
    numbers = range(1, 34)
    lottery_numbers = random.sample(numbers, 6)
    lottery_number = ' '.join(str(n) for n in lottery_numbers)
    lottery_time = datetime.now()
    record = LotteryRecord(lottery_number=lottery_number, lottery_time=lottery_time)
    db.session.add(record)
    db.session.commit()
    purchase_records = PurchaseRecord.query.all()
    for purchase_record in purchase_records:
        if purchase_record.ticket_number == lottery_number:
            winning_record = WinningRecord(user_id=purchase_record.user_id, ticket_number=purchase_record.ticket_number, lottery_number=lottery_number, winning_time=lottery_time)
            db.session.add(winning_record)
    db.session.commit()
    return '开奖成功'

if __name__ == '__main__':
    app.run()

4. 实现查询往期中奖号码功能

查询最近3期中奖号码可以用SQLAlchemy来查询中奖记录表，并按照中奖时间降序排序，取前3条记录。

代码示例：

from flask import Flask, jsonify
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///lottery.db'
db = SQLAlchemy(app)

class WinningRecord(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    user_id = db.Column(db.Integer)
    ticket_number = db.Column(db.String(20))
    lottery_number = db.Column(db.String(20))
    winning_time = db.Column(db.DateTime)

@app.route('/history')
def lottery_history():
    records = WinningRecord.query.order_by(WinningRecord.winning_time.desc()).limit(3).all()
    history = [{'lottery_number': r.lottery_number, 'winning_time': str(r.winning_time)} for r in records]
    return jsonify(history)

if __name__ == '__main__':
    app.run()

以上是一个简单的双色球系统的实现方案，具体可以根据实际情况进行调整和优化。