运行对同一个 table 的两个查询并在同一路由上实现它们

Question

我怎样才能使这个工作？

我想我应该使用 promises，但我对它们知之甚少。我读过它们，但无法创建应有的结构。

我只想运行对同一个 table 两个不同的查询，并在同一个 ejs 文件上使用返回值

app.get('/', (req, res) => {

    db.query('SELECT COUNT(*) AS count, FORMAT(SUM(donation_amount),2) AS total FROM donations;', (err, result) => {
        if (err) throw err;
        let count = result[0].count; //since query column is requested as "count". we can use "count" to get back the raw value
        let total = result[0].total;
        res.render('home', { count: count, total: total }); // just the file name is enough. ejs engine looks up the file name in the "views" folder
    });

    db.query('SELECT CONCAT(first_name, ", ", last_name AS latest_donator, donation_amount AS amount FROM donations ORDER BY donation_time LIMIT 1;', (err, result) => {
        if (err) throw err;
        let donatorName = result[0].latest_donator;
        let amount = result[0].amount;
        res.render('home', {first_name: donatorName, amount: amount});
    });
 });

Answer 1

您只有在获得两个查询的结果后才能发送响应 (res.render(...))。因此，您可能希望像这样按顺序执行它们。

app.get('/', (req, res) => {
    db.query('SELECT COUNT(*) AS count, FORMAT(SUM(donation_amount),2) AS total FROM donations;', (err, result) => {
        if (err) throw err;
        let count = result[0].count; //since query column is requested as "count". we can use "count" to get back the raw value
        let total = result[0].total;
        db.query('SELECT CONCAT(first_name, ", ", last_name AS latest_donator, donation_amount AS amount FROM donations ORDER BY donation_time LIMIT 1;', (err, result) => {
            if (err) throw err;
            let donatorName = result[0].latest_donator;
            let amount = result[0].amount;
            res.render('home', { first_name: donatorName, amount: amount, count: count, total: total });
        });
    });
});

但是查询彼此独立，因此您可以运行它们并行。

运行对同一个 table 的两个查询并在同一路由上实现它们

Running two queries on the same table and implement them on the same route

javascript

mysql

ejs

node.js

express

运行 对同一个 table 的两个查询并在同一路由上实现它们

Running two queries on the same table and implement them on the same route

javascript

mysql

ejs

node.js

express

运行对同一个 table 的两个查询并在同一路由上实现它们