查找班级平均值和每个科目的学生数量

const express = require('express');
const mysql = require('mysql');

const app = express();

// 创建数据库连接
const connection = mysql.createConnection({
  host: '数据库主机地址',
  user: '数据库用户名',
  password: '数据库密码',
  database: '数据库名'
});

// 连接数据库
connection.connect();

// 定义API接口
app.get('/class', (req, res) => {
  // 查询班级平均值
  connection.query('SELECT AVG(成绩) AS 平均值 FROM students', (error, results) => {
    if (error) throw error;
    const average = results[0].平均值;

    // 查询每个科目的学生数量
    connection.query('SELECT 科目, COUNT(*) AS 学生数量 FROM students GROUP BY 科目', (error, results) => {
      if (error) throw error;
      const subjects = results;

      // 返回结果
      res.json({ average, subjects });
    });
  });
});

// 启动服务器
app.listen(3000, () => {
  console.log('Server is running on port 3000');
});