SQL进阶---第二单元(第一到第四课)、Queries


SQL进阶---第二单元(第一到第四课)、Manipulation
第二单元、Queries
第十一课、SELECT

QUERIES Queri

In this lesson you will be learningdifferent SQLcommands to query a single table in
a database.

One of the core purposes of the SQL language is to retrieveinformation stored in a database. This is commonly referred to as querying.Queries
allow us to communic-ate with the database by asking questions and having theresult set return data releva-nt
to the question.
In this lesson, you will be querying a database with one tablenamed

movies

.
Let's getstarted.

Instructions

1、Let's
take a look at the nameand imdb_rating of
every movie in thedatabase.

In the code editor type

SELECT name,imdb_ratin

FROM movies;
SELECT name,imdb_rating
FROM movies;

QueryResults

name	imdb_rating
Avatar	7.9
Jurassic World	7.3
The Avengers	8.1
The Dark Knight	9.0
Star Wars: Episode I - The Phantom Menace	6.6
Star Wars	8.7
Avengers: Age of Ultron	7.9
The Dark Knight Rises	8.5
Pirates of the Caribbean: Dead Mans Chest	7.3
Iron Man 3	7.3
Spider-Man	7.3
Transformers: Revenge of the Fallen	6.0
Star Wars: Episode III - Revenge of the Sith	7.7
Spider-Man 2	7.3
Transformers: Dark of the Moon	6.3
American Sniper	7.4
Furious Seven	7.4
Spider-Man 3	6.2
Guardians of the Galaxy	8.1
Transformers	7.1
Iron Man	7.9
Indiana Jones and the Kingdom of the Crystal Skull	6.2
Iron Man 2	7.1
Star Wars: Episode II - Attack of the Clones	6.7
Pirates of the Caribbean: At Worlds End	7.1
Star Wars: Episode VI - Return of the Jedi	8.4
Independence Day	6.9
Pirates of the Caribbean: The Curse of the Black Pearl	8.1
Skyfall	7.8
Inception	8.8
Man of Steel	7.2
Star Wars: Episode V - The Empire Strikes Back	8.8
The Matrix Reloaded	7.2
The Amazing Spider-Man	7.1
The Incredibles	8.0
Captain America: The Winter Soldier	7.8
The Lego Movie	7.8
Star Trek	8.0
Batman	7.6
Night at the Museum	6.4
Transformers: Age of Extinction	5.8
Twister	6.3
Maleficent	7.0
Pirates of the Caribbean: On Stranger Tides	6.7
Fast & Furious 6	7.2
Beverly Hills Cop	7.3
X-Men: The Last Stand	6.8
X-Men: Days of Future Past	8.1
The Lost World: Jurassic Park	6.5
Star Trek Into Darkness	7.8
Shrek 2	7.2
Toy Story 3	8.4
Frozen	7.6
Finding Nemo	8.2
Despicable Me 2	7.5
Inside Out	8.6
Shrek the Third	6.0
Minions	6.7
Up	8.3
Monsters, Inc.	8.1
Home Alone	7.4
Meet the Fockers	6.3
The Hangover	7.8
Monsters University	7.4
Shrek	7.9
How the Grinch Stole Christmas	6.0
The Hangover Part II	6.5
Despicable Me	7.7
Men in Black	7.2
Toy Story 2	7.9
Cars	7.2
Bruce Almighty	6.7
My Big Fat Greek Wedding	6.6
Shrek Forever After	6.4
Brave	7.2
Ghostbusters	7.8
Rush Hour 2	6.6
Big Hero 6	7.9
Alvin and the Chipmunks: The Squeakquel	4.4
Mrs. Doubtfire	6.9
Ted	7.0
Aladdin	8.0
Alvin and the Chipmunks	5.3
Madagascar 3: Europes Most Wanted	7.0
Kung Fu Panda	7.6
The Lorax	6.5
Austin Powers in Goldmember	6.2
Back to the Future	8.5
Wedding Crashers	7.0
Charlie and the Chocolate Factory	6.7
Ratatouille	8.0
Austin Powers: The Spy Who Shagged Me	6.6
Tangled	7.8
Monsters vs. Aliens	6.6
Happy Feet	6.5
Ice Age: Dawn of the Dinosaurs	7.0
Ice Age: The Meltdown	6.9
World War Z	7.0
What Lies Beneath	6.6
Gremlins	7.2
The Blair Witch Project	6.4
The Conjuring	7.5
The Ring	7.1
The Grudge	5.9
Paranormal Activity	6.3
Interview with the Vampire: The Vampire Chronicles	7.6
Paranormal Activity 3	5.9
Scream	7.2
Jaws 2	5.7
Scream 2	6.1
Sleepy Hollow	7.4
The Others	7.6
The Haunting	4.9
Scream 3	5.5
Saw II	6.6
The Amityville Horror	6.2
Aliens	8.4
Paranormal Activity 2	5.7
Annabelle	5.4
Scooby-Doo 2: Monsters Unleashed	4.9
Insidious: Chapter 2	6.6
Dracula	7.5
Freddy vs. Jason	5.8
Blade II	6.7
Saw III	6.2
The Texas Chainsaw Massacre	6.2
Cloverfield	7.1
Dark Shadows	6.2
The Ring Two	5.4
Zombieland	7.7
Constantine	6.9
The Exorcism of Emily Rose	6.7
I Know What You Did Last Summer	5.6
1408	6.8
Mama	6.2
The Purge: Anarchy	6.5
Scary Movie 2	5.2
Blade	7.1
End of Days	5.7
The Forgotten	5.8
The Final Destination	5.2
Warm Bodies	6.9
Anaconda	4.6
Wolf	6.2
Friday the 13th	5.6
The Purge	5.6
Titanic	7.7
Forrest Gump	8.8
The Twilight Saga: Eclipse	4.9
The Twilight Saga: New Moon	4.6
The Twilight Saga: Breaking Dawn - Part 2	5.6
The Twilight Saga: Breaking Dawn - Part 1	4.9
Beauty and the Beast	8.0
King Kong	7.3
Ghost	7.0
Cinderella	7.1
Gone with the Wind	8.2
Pearl Harbor	6.0
Twilight	5.2
Mr. & Mrs. Smith	6.5
Snow White and the Seven Dwarfs	7.7
What Women Want	6.4
Top Gun	6.8
Pretty Woman	6.9
Hitch	6.7
Tootsie	7.4
Theres Something About Mary	7.1
Elf	6.9
Tarzan	7.2
Bridesmaids	6.8
Fifty Shades of Grey	4.2
Robin Hood: Prince of Thieves	6.9
The Proposal	6.7
The Sound of Music	8.0
Jerry Maguire	7.3
Sex and the City	5.5
Runaway Bride	5.4
Les Misérables	7.6
Knocked Up	7.1
Little Fockers	5.5
As Good as It Gets	7.8
American Pie 2	6.4
The Great Gatsby	7.3
Mamma Mia!	6.4
Juno	7.5
Marley & Me	7.1
Pocahontas	6.6
Slumdog Millionaire	8.0
Look Whos Talking	5.8
Click	6.4
The Lion King	8.5
Harry Potter and the Deathly Hallows: Part 2	8.1
The Sixth Sense	8.2
Jaws	8.1
I Am Legend	7.2
The Blind Side	7.7
Cast Away	7.7
Signs	6.7
Saving Private Ryan	8.6
Dawn of the Planet of the Apes	7.7
Interstellar	8.7
Gladiator	8.5
Dances with Wolves	8.0
The Perfect Storm	6.4
Lincoln	7.4
Rise of the Planet of the Apes	7.6
The Karate Kid	6.2
Rain Man	8.0
Air Force One	6.4
True Grit	7.7
A Beautiful Mind	8.2
The Help	8.1
3 Men and a Baby	5.9
Gone Girl	8.2
Kung Fu Panda 2	7.3
Hannibal	6.7
Catch Me If You Can	8.0
Big Daddy	6.4
Se7en	8.6
Seven	6.1

DatabaseSchema

movies 220 rows
id	INTEGER
name	TEXT
genre	TEXT
year	INTEGER
imdb_rating	REAL

第十二课、Select-l

QUERIES Select-II

SELECT name, imdb_rating

FROM movies;

In Lesson 1 you learned that

SELECT

is
used every time you wantto query data from a database.

Multiplecolumns can be queried at once by separating column names with a comma. By specifying

name,
imdb_rating

, the result set contains a

name

and

imdb_rating

column.
Instructions

1.Let's continue with the

SELECT

statement.
In the code editor, type

SELECT DISTINCT genre

FROM movies;

SELECT DISTINCT genre
FROM movies;

QueryResults

genre

action

comedy

horror

romance

drama

DatabaseSchema

movies 220 rows
id	INTEGER
name	TEXT
genre	TEXT
year	INTEGER
imdb_rating	REAL

第十三课、Select
Distinct

QUERIES Select Distinct

SELECT DISTINCT genre

FROM movies;

SELECT DISTINCT

is
used to return uniquevalues in the result set. It filters out all duplicate values. Here, the result set lists each genre in the

movies

table
exactly once.
1.

SELECT
DISTINCT

specifies that the statementis
going to be a query that returns unique values in the specified column(s)
2.

genre

is
the name of the column to display in the result set.
3.

FROM
movies

indicates the table name to query fro

Filtering the results of a query is an important skill in SQL.It is easier to see the different possible genres a movie can have after thedata has been filtered, than to scan
every row in the table.

The rest of this lesson willteach you different commands in SQL to filter the results of a query.
1.The
way tofilter queries in SQL is to use the

WHERE

clause.
In thecode editor type

SELECT * FROM moviesWHERE imdb_rating > 8;

SELECT * FROM movies
WHEREimdb_rating > 8;

QueryResults

id	name	genre	year	imdb_rating
3	The Avengers	action	2012	8.1
4	The Dark Knight	action	2008	9.0
6	Star Wars	action	1977	8.7
8	The Dark Knight Rises	action	2012	8.5
19	Guardians of the Galaxy	action	2014	8.1
26	Star Wars: Episode VI - Return of the Jedi	action	1983	8.4
28	Pirates of the Caribbean: The Curse of the Black Pearl	action	2003	8.1
30	Inception	action	2010	8.8
32	Star Wars: Episode V - The Empire Strikes Back	action	1980	8.8
48	X-Men: Days of Future Past	action	2014	8.1
52	Toy Story 3	comedy	2010	8.4
54	Finding Nemo	comedy	2003	8.2
56	Inside Out	comedy	2015	8.6
59	Up	comedy	2009	8.3
60	Monsters, Inc.	comedy	2001	8.1
88	Back to the Future	comedy	1985	8.5
117	Aliens	horror	1986	8.4
148	Forrest Gump	romance	1994	8.8
157	Gone with the Wind	romance	1939	8.2
191	The Lion King	drama	1994	8.5
192	Harry Potter and the Deathly Hallows: Part 2	drama	2011	8.1
193	The Sixth Sense	drama	1999	8.2
194	Jaws	drama	1975	8.1
199	Saving Private Ryan	drama	1998	8.6
201	Interstellar	drama	2014	8.7
202	Gladiator	drama	2000	8.5
211	A Beautiful Mind	drama	2001	8.2
212	The Help	drama	2011	8.1
214	Gone Girl	drama	2014	8.2
219	Se7en	drama	1995	8.6

DatabaseSchema

Movies 220 rows
id	INTEGER
name	TEXT
genre	TEXT
year	INTEGER
imdb_rating	REAL

第十四课、Where

QUERIES Where

SELECT * FROM movies

WHERE imdb_rating > 8;

This statement filters the result set to only include movieswith IMDb ratings greater than 8. How does it work?

WHERE

is
a clause that indicatesyou want to filter the result set to include only rows where the following condition is true.

2.

imdb_rating>
8

is a condition that filters theresult set. Here, only rows with
a value greater than 8 in the

imdb_rating

column
will be returned in the result set.
3.

>

is
an operator. Operators create a condition that can be evaluated as eithertrue or false.

Commonoperators used with the

WHERE

clause
are；

=

equals

!=

not
equals

>

greater
than

<

less
than

>=

greater
than or equal to

<=

less
than or equal to

There are also some specialoperators that we will learn more about in the upcoming exercises.

Instructions

1.

LIKE

is
a special operator that can be used in a

WHERE

clause.
In the code editor type

SELECT * FROM movies

WHERE name LIKE 'Se_en';

SELECT * FROM movies
WHEREname LIKE 'Se_en';

QueryResults

id	name	genre	year	imdb_rating
219	Se7en	drama	1995	8.6
220	Seven	drama	1979	6.1

DatabaseSchema

Movies 220 rows
id	INTEGER
name	TEXT
genre	TEXT
year	INTEGER
imdb_rating	REAL