node.js+express去连接sql server数据库，并创建连接池；使用axios实现前后端数据通信并实现对数据库的增删改查

首先，安装必要的npm包：

npm install express mssql axios body-parser --save

接下来，创建一个app.js文件：

const express = require('express');
const bodyParser = require('body-parser');
const mssql = require('mssql');
const axios = require('axios');

const app = express();

// 配置body-parser
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: true }));

// 配置mssql连接池
const pool = new mssql.ConnectionPool({
    user: 'username',
    password: 'password',
    server: 'localhost',
    database: 'database',
    pool: {
        max: 10,
        min: 0,
        idleTimeoutMillis: 30000
    }
});

// 测试连接池是否正常工作
pool.connect().then(() => {
    console.log('Connected to MSSQL');
}).catch(err => {
    console.log(err);
});

// 实现路由
app.get('/users', (req, res) => {
    pool.request()
        .query('SELECT * FROM users')
        .then(result => {
            res.json(result.recordset);
        })
        .catch(err => {
            console.log(err);
            res.status(500).send('Server Error');
        });
});

app.post('/users', (req, res) => {
    const { name, age, email } = req.body;

    pool.request()
        .input('name', name)
        .input('age', age)
        .input('email', email)
        .query('INSERT INTO users (name, age, email) VALUES (@name, @age, @email)')
        .then(() => {
            res.send('User added');
        })
        .catch(err => {
            console.log(err);
            res.status(500).send('Server Error');
        });
});

app.put('/users/:id', (req, res) => {
    const { name, age, email } = req.body;
    const { id } = req.params;

    pool.request()
        .input('id', id)
        .input('name', name)
        .input('age', age)
        .input('email', email)
        .query('UPDATE users SET name = @name, age = @age, email = @email WHERE id = @id')
        .then(() => {
            res.send('User updated');
        })
        .catch(err => {
            console.log(err);
            res.status(500).send('Server Error');
        });
});

app.delete('/users/:id', (req, res) => {
    const { id } = req.params;

    pool.request()
        .input('id', id)
        .query('DELETE FROM users WHERE id = @id')
        .then(() => {
            res.send('User deleted');
        })
        .catch(err => {
            console.log(err);
            res.status(500).send('Server Error');
        });
});

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

// 测试axios前后端数据通信
axios.get('http://localhost:3000/users')
    .then(res => console.log(res.data))
    .catch(err => console.log(err));

axios.post('http://localhost:3000/users', { name: 'John', age: 30, email: 'john@example.com' })
    .then(res => console.log(res.data))
    .catch(err => console.log(err));

axios.put('http://localhost:3000/users/1', { name: 'John Doe', age: 32, email: 'johndoe@example.com' })
    .then(res => console.log(res.data))
    .catch(err => console.log(err));

axios.delete('http://localhost:3000/users/1')
    .then(res => console.log(res.data))
    .catch(err => console.log(err));

注意：在使用mssql连接池之前，需要先安装mssql的驱动程序：

npm install mssql --save

运行node app.js，即可启动服务器。使用axios发送请求，即可对数据库进行增删改查操作。