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What is the purpose of a session store? like DynamoDB for example.
Can someone enlighten me on what is the difference between Join and Union and when should each be used?
I got asked that in todays interview for a php backend developer job
I somehow made it to the second part of the interview (they will give me a shitton of tables and ask me to show them rows from a lot of tables)
dumb question, but how come I can't rename url or method to anything else in this case
app.use((req, res, next) => {
const {url, method} = req;
const time = new Date();
const message = `${method}: ${url} - ${time}`;
console.log(message);
});
I thought this is creating two variables and assigning the first two values of the req object to them? Why do they become undefined if I called one something like method 2 IN BOTH references?
Am I retarded?
>Is middleware in expressjs basically just the code that actually does something with the res/req? And express is just a framework that allows the application to receive/send http messages?
That's basically correct yes. Though middle-ware is more like any module that can hook and process some bit of Express without getting in the way too much, things like the body-parser are also middle-ware, as is passport. Though technically, they really just 'do something with the req' too so your description is pretty accurate even if it does cover a lot of things that you might not think of as explicitly handling the request/response.
>Can someone enlighten me on what is the difference between Join and Union and when should each be used?
I think you mean in the context of SQL.
A union just adds the results of two different queries and makes it look like one query. So, query A returns 4 rows, query B returns 6 rows, (A UNION B) returns 10 rows. If the columns aren't identical in both queries then it comes down to the SELECT line to see what gets returned but otherwise, some columns will be null in one set or the other.
A join connects two tables and then the query gets one set of results from them, usually we join things in the sense of:
SELECT patient.patient_id, patient.first_name, patient.last_name, patiend.dob, doctor.last_name, doctor.first_name, appointment.date_time FROM patient
LEFT JOIN appointment ON patient.patient_id = appointment.patient_id
LEFT JOIN doctor ON doctor.doctor_id = appointment.doctor_id
That connects the three tables together (technically, it connects the first two tables and then connects the result to the third table) using the primary/foreign keys named, you don't have to use keys either though you usually should.
Generally, UNION is used to connect queries that are the same shape, JOIN to create connected queries.
>how come I can't rename url or method to anything else in this case
You initialized them as const. You can't change the value of a const.
Also const and let variables only exist in the blocks they are defined, if you want a global variable, initialize them as var.
just google it
Thanks a lot, user.
I've had ton of fun learning php and mysql by myself in these 3 weeks(4 hours each day reading docs, watching tutorials in youtube and coding any stuff by myself) to the point of being confident enough to apply for a backend job but after this interview, I feel I have a loooot of stuff to learn about php and sql in general.
you applied for a job after 3 weeks and got an interview? What the fuck?