pre-view/CS50-raw · Datasets at Hugging Face

text stringlengths 1 81	start float64 0 10.1k	duration float64 0 24.9
I now see I'm down to two paintings, two pieces of artwork that	2,705.87	4.95
were acquired only after 1909.	2,710.82	4.9
OK, so given this part on DELETE, we're able to delete one row or even multiple	2,715.72	7.47
rows at a time.	2,723.19	1.125
But there are still instances where you might	2,724.315	1.875
want to think about, should we delete something or can we delete something.	2,726.19	4.89
We'll talk about those in just a minute in terms of constraints.	2,731.08	3.93
We back in a few.	2,735.01	1.17
And we're back.	2,736.18	1.68
So we just saw how to delete one row, even multiple rows.	2,737.86	5.4
We haven't yet talked about whether we should delete some data	2,743.26	3.36
or whether we should delete some data and particularly	2,746.62	2.4
in the context of these constraints, where	2,749.02	2.16
you might have maybe a piece of data you actually	2,751.18	2.16
shouldn't delete to maintain the integrity of your table.	2,753.34	4.12
Now, one example of this is a [? Foreign ?] [? Key ?]	2,757.46	3.41
[? Constraint, ?] which means that you have some table with a primary key that	2,760.87	5.01
is referenced by some other table.	2,765.88	2.283
And we'll get concrete about this in a minute.	2,768.163	1.917
But it might mean that if you were to delete that primary key,	2,770.08	3.3
that other table would have nothing to reference.	2,773.38	2.83
So let's update our schema here for the MFA, the Museum of Fine Arts.	2,776.21	4.4
And let's say that they have not just a collection now, but also artists	2,780.61	4.53
involved.	2,785.14	0.75
And there exists a [? many ?] [? to ?] [? many ?] relationship among artists	2,785.89	4.08
and items in the collection.	2,789.97	2.19
We could say that an artist might make more than one piece of art	2,792.16	4.32
in the collection.	2,796.48	1.23
And a piece of art might be created by more than one artist.	2,797.71	4.77
Now concretely in our database, this might look as follows.	2,802.48	4.57
I could have a table for artists and a table for collections.	2,807.05	4.43
And notice how each has their own primary key.	2,811.48	3.3
Artists has an id column, called our primary key column.	2,814.78	3.33
Collections too has an id called our primary key column here.	2,818.11	4.29
Now, in the middle is this table created that symbolizes,	2,822.4	4.02
that represents the relationship among artists and items in the collection.	2,826.42	4.86
Here on the first row, we see the artist id of 1 created the piece of art	2,831.28	5.1
with the collection id of 2.	2,836.38	2.37
So who did what here?	2,838.75	2.08
Well, we can see that the artist with the ID of 1 is Li Yin.	2,840.83	4.37
Li Yin created this piece of art, the id of 2, which is Imaginative landscape.	2,845.2	6.54
So we can kind of relate in this case artists with collections	2,851.74	3.6
as we saw just a few weeks ago.	2,855.34	2.55
But let's say we decide to delete a particular artist,	2,857.89	3.99
maybe we delete Unidentified artists down here.	2,861.88	3.63
Well, we could just delete from the artist table.	2,865.51	2.59
Maybe we find a condition to select this row and we delete from artists.	2,868.1	5.84
We'll do that here remove that row.	2,873.94	2.67
But what have we done wrong?	2,876.61	2.91
If we look at our created table in particular,	2,879.52	4.04
what have we now done wrong?	2,883.56	2.79
What kind of problem might we [? run ?] [? into? ?] Let's go to [? Karim. ?]	2,886.35	7.51
SPEAKER 11: [? Yeah ?] [INAUDIBLE] [? was ?] [? only ?] [? deleted ?]	2,893.86	3.455
[? from ?] [? the ?] [? artist ?] [INAUDIBLE] without the other	2,897.315	2.625
[INAUDIBLE].	2,899.94	0.813
SPEAKER 1: Yeah, good point.	2,900.753	1.167
We only deleted the artist with the id of 3 from the artists table.	2,901.92	5.73
Now if I look at the created table and I look for the artist with id of 3,	2,907.65	6.693
do you see them?	2,914.343	0.667
They don't exist anymore.	2,915.01	1.18
So I can't understand this relationship.	2,916.19	2
I don't know the artist with the id of 3.	2,918.19	3.93
So let's try this now with a new kind of schema now in our database.	2,922.12	5.67
I'll go back to my computer.	2,927.79	2.49
And let me open up our new version of our database.	2,930.28	3.57
I'll type sqlite3, in this case, mfa.db, same name, but now a different schema.	2,933.85	7.59
If I type .schema, notice a few things here.	2,941.44	4.2
I have those same tables we saw visually.	2,945.64	3.45
I have collections, artists, and a created table.	2,949.09	4.65
And [? let me ?] focus in particular on this created table.	2,953.74	2.94
If I say .schema, in this case, created, Enter,	2,956.68	4.41
I'll see I have a FOREIGN KEY constraint on my "artist_id"	2,961.09	5.52
column and my "collection_id" column.	2,966.61	3.43
So if I tried to delete an artist that is referenced in my created table,	2,970.04	6.26
I would probably raise a constraint error--	2,976.3	3.69
a FOREIGN KEY [? constraint ?] error.	2,979.99	2.38
So let's just try this and see what happens.	2,982.37	3.3
Let me try DELETE FROM the [? artist's ?] [? table, ?] DELETE FROM	2,985.67	4.88
"artists" WHERE, let's say the "name" of the artist is literally "Unidentified	2,990.55	8.51
artist."	2,999.06	0.88
This is the name they have in the Museum of Fine Arts collections--	2,999.94	3.62
Unidentified artist.	3,003.56	1.71
So now I want to delete them from that table.	3,005.27	3
Well, if I hit Enter, I do get that FOREIGN KEY constraint error.	3,008.27	5.86
So does this mean I just can't delete this artist or is there a workaround?	3,014.13	5.48
Let's look at it visually again.	3,019.61	1.68
I'll go back to what we had before as our table,	3,021.29	3.45
and let me ask the audience here.	3,024.74	2.88
What's the solution?	3,027.62	1.59
If I can't delete Unidentified artist, because they	3,029.21	3.93
have an id referenced by this table, what should I maybe do first?	3,033.14	5.16
What should I do instead?	3,038.3	1.395
SPEAKER 12: Yeah, I want to say that first we	3,039.695	1.875
can delete the id that is being referenced by this [? id ?]	3,041.57	4.59
that we want to delete, then we can delete it.	3,046.16	2.58
In fact, if we want to delete it from the artists,	3,048.74	2.43
first we have to delete from the created table [INAUDIBLE] table, which	3,051.17	3.78
it is referencing, then we can delete from the artist [INAUDIBLE]	3,054.95	3.12
SPEAKER 1: Yeah, I like your thinking here.	3,058.07	1.99
So if we look at the created table, you notice	3,060.06	2.42

I now see I'm down to two paintings, two pieces of artwork that

2,705.87

4.95

were acquired only after 1909.

2,710.82

4.9

OK, so given this part on DELETE, we're able to delete one row or even multiple

2,715.72

7.47

rows at a time.

2,723.19

1.125

But there are still instances where you might

2,724.315

1.875

want to think about, should we delete something or can we delete something.

2,726.19

4.89

We'll talk about those in just a minute in terms of constraints.

2,731.08

3.93

We back in a few.

2,735.01

1.17

And we're back.

2,736.18

1.68

So we just saw how to delete one row, even multiple rows.

2,737.86

5.4

We haven't yet talked about whether we should delete some data

2,743.26

3.36

or whether we should delete some data and particularly

2,746.62

2.4

in the context of these constraints, where

2,749.02

2.16

you might have maybe a piece of data you actually

2,751.18

2.16

shouldn't delete to maintain the integrity of your table.

2,753.34

4.12

Now, one example of this is a [? Foreign ?] [? Key ?]

2,757.46

3.41

[? Constraint, ?] which means that you have some table with a primary key that

2,760.87

5.01

is referenced by some other table.

2,765.88

2.283

And we'll get concrete about this in a minute.

2,768.163

1.917

But it might mean that if you were to delete that primary key,

2,770.08

3.3

that other table would have nothing to reference.

2,773.38

2.83

So let's update our schema here for the MFA, the Museum of Fine Arts.

2,776.21

4.4

And let's say that they have not just a collection now, but also artists

2,780.61

4.53

involved.

2,785.14

0.75

And there exists a [? many ?] [? to ?] [? many ?] relationship among artists

2,785.89

4.08

and items in the collection.

2,789.97

2.19

We could say that an artist might make more than one piece of art

2,792.16

4.32

in the collection.

2,796.48

1.23

And a piece of art might be created by more than one artist.

2,797.71

4.77

Now concretely in our database, this might look as follows.

2,802.48

4.57

I could have a table for artists and a table for collections.

2,807.05

4.43

And notice how each has their own primary key.

2,811.48

3.3

Artists has an id column, called our primary key column.

2,814.78

3.33

Collections too has an id called our primary key column here.

2,818.11

4.29

Now, in the middle is this table created that symbolizes,

2,822.4

4.02

that represents the relationship among artists and items in the collection.

2,826.42

4.86

Here on the first row, we see the artist id of 1 created the piece of art

2,831.28

5.1

with the collection id of 2.

2,836.38

2.37

So who did what here?

2,838.75

2.08

Well, we can see that the artist with the ID of 1 is Li Yin.

2,840.83

4.37

Li Yin created this piece of art, the id of 2, which is Imaginative landscape.

2,845.2

6.54

So we can kind of relate in this case artists with collections

2,851.74

3.6

as we saw just a few weeks ago.

2,855.34

2.55

But let's say we decide to delete a particular artist,

2,857.89

3.99

maybe we delete Unidentified artists down here.

2,861.88

3.63

Well, we could just delete from the artist table.

2,865.51

2.59

Maybe we find a condition to select this row and we delete from artists.

2,868.1

5.84

We'll do that here remove that row.

2,873.94

2.67

But what have we done wrong?

2,876.61

2.91

If we look at our created table in particular,

2,879.52

4.04

what have we now done wrong?

2,883.56

2.79

What kind of problem might we [? run ?] [? into? ?] Let's go to [? Karim. ?]

2,886.35

7.51

SPEAKER 11: [? Yeah ?] [INAUDIBLE] [? was ?] [? only ?] [? deleted ?]

2,893.86

3.455

[? from ?] [? the ?] [? artist ?] [INAUDIBLE] without the other

2,897.315

2.625

[INAUDIBLE].

2,899.94

0.813

SPEAKER 1: Yeah, good point.

2,900.753

1.167

We only deleted the artist with the id of 3 from the artists table.

2,901.92

5.73

Now if I look at the created table and I look for the artist with id of 3,

2,907.65

6.693

do you see them?

2,914.343

0.667

They don't exist anymore.

2,915.01

1.18

So I can't understand this relationship.

2,916.19

2

I don't know the artist with the id of 3.

2,918.19

3.93

So let's try this now with a new kind of schema now in our database.

2,922.12

5.67

I'll go back to my computer.

2,927.79

2.49

And let me open up our new version of our database.

2,930.28

3.57

I'll type sqlite3, in this case, mfa.db, same name, but now a different schema.

2,933.85

7.59

If I type .schema, notice a few things here.

2,941.44

4.2

I have those same tables we saw visually.

2,945.64

3.45

I have collections, artists, and a created table.

2,949.09

4.65

And [? let me ?] focus in particular on this created table.

2,953.74

2.94

If I say .schema, in this case, created, Enter,

2,956.68

4.41

I'll see I have a FOREIGN KEY constraint on my "artist_id"

2,961.09

5.52

column and my "collection_id" column.

2,966.61

3.43

So if I tried to delete an artist that is referenced in my created table,

2,970.04

6.26

I would probably raise a constraint error--

2,976.3

3.69

a FOREIGN KEY [? constraint ?] error.

2,979.99

2.38

So let's just try this and see what happens.

2,982.37

3.3

Let me try DELETE FROM the [? artist's ?] [? table, ?] DELETE FROM

2,985.67

4.88

"artists" WHERE, let's say the "name" of the artist is literally "Unidentified

2,990.55

8.51

artist."

2,999.06

0.88

This is the name they have in the Museum of Fine Arts collections--

2,999.94

3.62

Unidentified artist.

3,003.56

1.71

So now I want to delete them from that table.

3,005.27

3

Well, if I hit Enter, I do get that FOREIGN KEY constraint error.

3,008.27

5.86

So does this mean I just can't delete this artist or is there a workaround?

3,014.13

5.48

Let's look at it visually again.

3,019.61

1.68

I'll go back to what we had before as our table,

3,021.29

3.45

and let me ask the audience here.

3,024.74

2.88

What's the solution?

3,027.62

1.59

If I can't delete Unidentified artist, because they

3,029.21

3.93

have an id referenced by this table, what should I maybe do first?

3,033.14

5.16

What should I do instead?

3,038.3

1.395

SPEAKER 12: Yeah, I want to say that first we

3,039.695

1.875

can delete the id that is being referenced by this [? id ?]

3,041.57

4.59

that we want to delete, then we can delete it.

3,046.16

2.58

In fact, if we want to delete it from the artists,

3,048.74

2.43

first we have to delete from the created table [INAUDIBLE] table, which

3,051.17

3.78

it is referencing, then we can delete from the artist [INAUDIBLE]

3,054.95

3.12

SPEAKER 1: Yeah, I like your thinking here.

3,058.07

1.99

So if we look at the created table, you notice

3,060.06

2.42