Question

我创建了到数据库的连接，该数据库中有许多与主题相关的表（例如：-subject1，subject2，subject3 ...）。

每个主题表都有两列，即'IndexNo，Result'。我想获得与相同索引号相关的结果。从每个表（一个学生为多个科目的成绩）并将其推入数组。怎么做？

这是我的代码，它返回许多错误。

    const mysql = require('mysql');

    var connect = mysql.createConnection({
    host:'localhost',
    user:'root',
    password:'',
    database:'results_center'
    });

    var studentid = 1234;
    var results = [];
    var i =0;
    for(i=1;i++;i<8){

        var newResult;
        connect.query("select result from subject"+i+" WHERE Index_No = " + studentid,(err,result)=>{
            newResult = result;
        });
            results[i] = result;
    }
      connect.end() 
      console.log(results);

Answer 1

将回调转换为promise并使用Promise.all获取所有结果。

const util = require('util');
const query = util.promisify(connect.query);


var i = 0;
var promises = [];
for(i=1;i++;i<8){
    promises.push(query("select result from subject"+i+" WHERE Index_No = " + studentid));
}

Promise.all(promises).then(results => {
  connect.end() 
  console.log(results);
})

Answer 2

var mysql = require('mysql');
var con = mysql.createConnection({
    host: 'localhost',
    user: 'root',
    password: '',
    database: 'results_center'
});

con.connect(function(err) {
    if (err) throw err;
    console.log("connected to mysql");

    var subjectResults = [];
    var studentid = 1234;
    var sql = '';

    var i = 0;
    for (i = 1; i++; i < 8) {
        sql = "select result from subject" + i + " WHERE Index_No = " + studentid;
        con.query(sql, function(err, results, fields) {
            subjectResults.push(results);
        });
    }
});

如何连接到数据库并从Node.js中的多个表获取数据？

2 个答案: