Question

我想访问包含计数元素实际数量的变量，但我不知道如何。

    sql = "SELECT COUNT(id) FROM users WHERE username='" + req.body.username + "' AND password='" + req.body.password + "';";
    con.query(sql, function (err, result) {
    if (err) throw err;
    })

result是：[ RowDataPacket { 'COUNT(id)': 0 } ]；我无法使用语法result.COUNT（id）访问数据，因为出现错误：ReferenceError: id is not defined

Answer 1

为count使用别名，为了更好地抽象，请在查询中使用模板文字

 sql = `SELECT COUNT(id) as count FROM users WHERE username=${req.body.username}  AND password=${req.body.password}`;
    con.query(sql, function (err, result) {
        if (err) throw err;
    })

对于[RowDataPacket {'total'：0}]，请尝试

     sql = `SELECT COUNT(id) as count FROM users WHERE username=${req.body.username}  AND password=${req.body.password}`;
            con.query(sql, function (err, result) {
                if (err) throw err;
                  else{
let results=JSON.parse(JSON.stringify(result)) // gives you an js object array
    } })

Answer 2

给您的字段一个别名（标签）

sql = "SELECT COUNT(id) as total FROM users WHERE username='" + req.body.username + "' AND password='" + req.body.password + "';";

结果将为[ RowDataPacket { 'total': 0 } ]

执行'SELECT COUNT'查询后，无法从RowDataPacket访问'COUNT（id）'

2 个答案: