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forgetful-elephant - 178 core sql solo #1

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c181b82
student table
Mar 8, 2017
14ca9bd
friend table
Mar 8, 2017
0961c4f
student like
Mar 8, 2017
14eeab2
loaded
Mar 8, 2017
db8605d
friends of a gabriel
Mar 9, 2017
6dc3a5a
13 - popular students
Mar 9, 2017
9e450bd
popular students
Mar 9, 2017
ca0c6fc
notLikedStudents
Mar 10, 2017
a1c069c
almost done
Mar 11, 2017
503169e
almost done
Mar 11, 2017
6350922
brushing up
Mar 11, 2017
7ab91e6
exercise 11
Mar 12, 2017
50372d6
final commit
Mar 13, 2017
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6 changes: 6 additions & 0 deletions sql/01-create-table-student.sql
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DROP TABLE IF EXISTS student;
CREATE TABLE student (
id SERIAL PRIMARY KEY,
name VARCHAR(255),
grade INTEGER
);
5 changes: 5 additions & 0 deletions sql/02-create-table-friend.sql
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DROP TABLE IF EXISTS friend;
CREATE TABLE friend (
id1 INTEGER REFERENCES student(id),
id2 INTEGER REFERENCES student(id),
);
5 changes: 5 additions & 0 deletions sql/03-create-table-like.sql
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DROP TABLE IF EXISTS student_like;
CREATE TABLE student_like (
liker_id INTEGER REFERENCES student(id),
likee_id INTEGER REFERENCES student(id),
);
16 changes: 16 additions & 0 deletions sql/04-load-table-student.sql
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INSERT INTO student VALUES (1510, 'Jordan', 9);
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@ghost ghost Mar 13, 2017

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This is a workaround from loading the CSV file directly. Different database systems have different ways of doing this (copy, load data infile), but it'll be good for you to learn the methods because sometimes you'll end up having to work with big files, or you will be automating things and so you won't want to write the code by hand.

INSERT INTO student VALUES (1689, 'Gabriel', 9);
INSERT INTO student VALUES (1381, 'Tiffany', 9);
INSERT INTO student VALUES (1709, 'Cassandra', 9);
INSERT INTO student VALUES (1101, 'Haley', 10);
INSERT INTO student VALUES (1782, 'Andrew', 10);
INSERT INTO student VALUES (1468, 'Kris', 10);
INSERT INTO student VALUES (1641, 'Brittany', 10);
INSERT INTO student VALUES (1274, 'Alexis', 11);
INSERT INTO student VALUES (1316, 'Austin', 11);
INSERT INTO student VALUES (1911, 'Gabriel', 11);
INSERT INTO student VALUES (1501, 'Jessica', 11);
INSERT INTO student VALUES (1304, 'Jordan', 12);
INSERT INTO student VALUES (1025, 'John', 12);
INSERT INTO student VALUES (1934, 'Kyle', 12);
INSERT INTO student VALUES (1661, 'Logan', 12);
20 changes: 20 additions & 0 deletions sql/05-load-table-friend.sql
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INSERT INTO friend VALUES (1510, 1381);
INSERT INTO friend VALUES (1510, 1689);
INSERT INTO friend VALUES (1689, 1709);
INSERT INTO friend VALUES (1381, 1247);
INSERT INTO friend VALUES (1709, 1247);
INSERT INTO friend VALUES (1689, 1782);
INSERT INTO friend VALUES (1782, 1468);
INSERT INTO friend VALUES (1782, 1316);
INSERT INTO friend VALUES (1782, 1304);
INSERT INTO friend VALUES (1468, 1101);
INSERT INTO friend VALUES (1468, 1641);
INSERT INTO friend VALUES (1101, 1641);
INSERT INTO friend VALUES (1247, 1911);
INSERT INTO friend VALUES (1247, 1501);
INSERT INTO friend VALUES (1911, 1501);
INSERT INTO friend VALUES (1501, 1934);
INSERT INTO friend VALUES (1316, 1934);
INSERT INTO friend VALUES (1934, 1304);
INSERT INTO friend VALUES (1304, 1661);
INSERT INTO friend VALUES (1661, 1025);
10 changes: 10 additions & 0 deletions sql/06-load-table-like.sql
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INSERT INTO student_like VALUES (1689, 1709);
INSERT INTO student_like VALUES (1709, 1689);
INSERT INTO student_like VALUES (1782, 1709);
INSERT INTO student_like VALUES (1911, 1247);
INSERT INTO student_like VALUES (1247, 1468);
INSERT INTO student_like VALUES (1641, 1468);
INSERT INTO student_like VALUES (1316, 1304);
INSERT INTO student_like VALUES (1501, 1934);
INSERT INTO student_like VALUES (1934, 1501);
INSERT INTO student_like VALUES (1025, 1101);
13 changes: 13 additions & 0 deletions sql/07-query-friends-gabriel.sql
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SELECT
name
FROM
student.student
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@ghost ghost Mar 13, 2017 •
edited by ghost
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This part looks fine, just wanted to comment that often in industry people would alias their tables here. E.g. "student.student s" would alias the table "s"

JOIN
student.friend
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This could be aliased too (for example f, or t2)

ON
student.student.id = student.friend.id1
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And here you could go s.id = f.id1

WHERE
id2 = 1911
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The spirit of this task is to query everyone who is friends with someone named Gabriel, so you would probably want the where clause to be on the name. Hardcoding it for the two student IDs of people named Gabriel is manual (so it's actually more work), and your query doesn't reflect the spirit of the question, and it will break if there are any new people named Gabriel. Ideally, someone would be able to tell what you're trying to do by reading your query.

OR
id2 = 1689;

21 changes: 21 additions & 0 deletions sql/08-query-likes-grade-two-or-more.sql
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SELECT
student_who_likes.name,
student_who_likes.grade,
student_who_is_liked.named
student_who_is_liked.grade
FROM
student
AS
student_who_likes
JOIN
student_like
ON
student_who_likes.id = student_like.liker_id
JOIN
student
AS
student_who_is_liked
ON
student_who_is_liked.id = student_like.likee_id
WHERE
student_who_likes.grade - student_who_is_liked.grade >= 1;
81 changes: 81 additions & 0 deletions sql/09-mutual-likes.sql
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SELECT DISTINCT
student1.name,
student1.grade,
student2.name,
student2.grade
FROM
student
AS
student1
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@ghost ghost Mar 13, 2017 •
edited by ghost
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This is fine! Just a comment - It's okay to make short aliases, like s1, or s2, etc. to make typing easier.

JOIN
student_like
ON
student1.id = student_like.liker_id
JOIN
student
AS
student2
ON
student_like.likee_id = student2.id
WHERE
student1.id IN (
SELECT likee_id FROM student_like
)
ORDER BY
student1.name;

































SELECT
first_name, grade
FROM
student
JOIN
student_like
AS
a_student_who_likes_b_student
ON
student.id = a_student_who_likes_b_student.liker_id
JOIN
student_like
AS
b_student_who_likes_a_student
ON
student.id = a_student_who_likes_b_student.likee_id

WHERE
(id
IN (SELECT
liker_id
FROM
student_like))
16 changes: 16 additions & 0 deletions sql/10-not-liked.sql
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SELECT
name, grade
FROM
student
WHERE
(id NOT
IN (SELECT
liker_id
FROM
student_like))
AND
(id NOT
IN (SELECT
likee_id
FROM
student_like));
25 changes: 25 additions & 0 deletions sql/11-liked-but-does-not-like.sql
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SELECT DISTINCT
student_a_who_likes_student_b.name,
student_a_who_likes_student_b.grade,
student_b_who_likes_no_one.name,
student_b_who_likes_no_one.grade
FROM
student
AS
student_a_who_likes_student_b
JOIN
student_like
ON
student_a_who_likes_student_b.id = student_like.liker_id
JOIN
student
AS
student_b_who_likes_no_one
ON
student_like.likee_id = student_b_who_likes_no_one.id
WHERE
student_b_who_likes_no_one.id NOT IN (
SELECT liker_id FROM student_like
)
ORDER BY
student_a_who_likes_student_b.name;
38 changes: 38 additions & 0 deletions sql/12-find-friends-in-common.sql
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SELECT DISTINCT
student_a.name,
student_a.grade,
student_b.name,
student_b.grade,
student_c.name,
student_c.grade
FROM
student
JOIN
student_like
ON
student.id = student_like.liker_id
JOIN
friend
ON
student_like.likee_id = friend.id1
JOIN
student
AS
student_a
ON
student_a.id = student_like.liker_id
JOIN
student
AS
student_b
ON
student_b.id = student_like.likee_id
JOIN
student
AS
student_c
ON
student_c.id = friend.id1
ORDER BY
student_a.first_name
LIMIT 2
12 changes: 12 additions & 0 deletions sql/13-popular-students.sql
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SELECT
name
FROM
student.student_like
JOIN
student.student
ON
student.student.id = student.student_like.likee_id
GROUP BY
name
HAVING
count(likee_id) >= 2;