Name: CS50 2017 - Lecture 10 - SQL
Uploaded: 2017-11-14T16:53:27.000Z
Duration: 1 h 45 min 22 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

DAVID MALAN: All right, this is CS50 and this is lecture 10.

Today, for those tuning in online, is freshmen family weekend.

We have quite a few guests with us and we

thought we would begin today in fact by perhaps putting everyone

at ease since I know this is perhaps the first time in a while

Maybe this is your first class for the fall semester.

And so we thought we'd share with you by proxy

what you might be feeling by way of a short film

that CS50's video team put together with a little friend of ours

DAVID MALAN: All right, well, welcome to Harvard and CS50.

So if you'd like to actually return in just a few weeks time,

your children or siblings or friends or here in the room

will be exhibiting their CS50 final projects in just a few weeks' time.

This is the so-called CS50 fair, which is

meant to be a campus wide exhibition of students' final projects.

And it's worth noting that, as the students in the class know,

68% of the students in CS50 this year had no prior CS experience.

And so what you and they will see on display at the CS fair

in a few weeks' time in December is all of their accomplishments.

And in fact, the goal of this event really

is to delight in what everyone has achieved and glancing

at each other's screens and phones to see with great surprise what

So you are invited back if you would like for that as well.

Now CS50 of course is characterized as a class

for those less comfortable and those more comfortable

And I daresay some of our guests today are perhaps

at one end of that spectrum or the other.

And so rest assured that what we'll dive into today,

the world of databases and SQL with applications to data science

and beyond, is new to most everyone in the room as well.

So you are in good company, and I daresay 68% or more

of percent of the parents in the room are perhaps feeling exactly as you are.

So if we can now turn our attention back to some things lower level,

those students among you will recall that we focused in recent days

on Python, this other higher level language by which you

can solve problems a bit more readily than you can using, say, something

lower level like C. Now you might have noticed I'm ready if you dived

into problem set 6 as I'm sure you have, the debug 50 only

So you have relatively fewer tools at your disposal for debugging.

But do realize that within the CS50 library for Python

is a function like this called eprint, which

you might recall if you've used eprintf with C.

And so if you need help debugging your programs,

it suffices to write a program in Python.

And anywhere you want to see diagnostic output,

And it will print the file name and the line number for which you

But let's turn our attention now to things more web-oriented

and perhaps something with which you're familiar Facebook

So there's so many websites out there today where when you visit them,

you're prompted to log in-- something like this.

But you're not prompted to log in every time you click a link on facebook.com.

You're not prompted to log in every minute or every two minutes

because indeed, the websites, if they required as much,

they would degrade into something downright unusable.

So instead, these websites remember that you're logged in somehow.

So you log in once per day, per week, per year.

And then somehow the website remembers that you are Maria or you are Brian

and you have already logged into this website.

How does Facebook or any site like it, Gmail and beyond,

remember that you are logged in once you are logged in even though you only

DAVID MALAN: OK, so they store information on the server.

On the server, as we're now starting to see with Python and today with SQL,

you have the ability to store information on a server.

We saw very simply about a week ago the ability to store data

in, like, CSV files, just text files on the server.

That's not going to be very high performing,

so we're going to do better than that today.

But you can also store data in variables inside a flask

But we'll need some more sophistication than that.

But yes, we can certainly remember that Maria or Brian have logged in.

But how do we remember from which computer or browser

DAVID MALAN: Via the IP address-- so could work.

You could just recall that from those virtual envelopes

We've been writing the to address in the from address, the IP address, on those

So you could certainly remember, oh, I saw Brian from 1.2.3.4 and Maria

Subtitles ListPlay Video

CS50 2017 - Lecture 10 - SQL

sort

instance

audience

unique