Query tables

.gitignore

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+.DS_Store

sql/01-create-table-student.sql

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 CREATE TABLE student (
-  id INT PRIMARY KEY,
-  name TEXT,
-  grade INT
+  id SERIAL PRIMARY KEY,
+  name VARCHAR(255),
+  grade INTEGER
 );

sql/02-create-table-friend.sql

@@ -1,4 +1,4 @@
 CREATE TABLE friend (
-  id1 INT REFERENCES STUDENT(ID),
-  id2 INT REFERENCES STUDENT(ID)
+  id1 INT REFERENCES student(id),
+  id2 INT REFERENCES student(id)
 );

sql/02-create-table-friend0.sql

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+CREATE TABLE friend (
+  id1 INT REFERENCES student(id),
+  id2 INT REFERENCES student(id)
+);

sql/02-create-table-friend1.sql

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+CREATE TABLE friend (
+  id1 INT REFERENCES student(id),
+  id2 INT REFERENCES student(id)
+);

sql/03-create-table-like.sql

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 CREATE TABLE student_like (
-  liker_id INT references student(ID),
-  likee_id INT references student(ID)
-); 
+  liker_id INT REFERENCES student(ID),
+  likee_id INT REFERENCES student(ID)
+);

sql/04-load-table-student.sql

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+COPY student
+FROM '/Users/kamilalambert/Desktop/Projects/sql-exercises/data/students.csv' DELIMITER ',' CSV HEADER;

sql/05-load-table-friend.sql

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+COPY friend
+FROM '/Users/kamilalambert/Desktop/Projects/sql-exercises/data/friends.csv' DELIMITER ',' CSV HEADER;

sql/06-load-table-like.sql

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+COPY student_like
+FROM '/Users/kamilalambert/Desktop/Projects/sql-exercises/data/likes.csv' DELIMITER ',' CSV HEADER;

sql/07-query-friends-gabriel.sql

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+-- Find the names of all students who are friends with someone named Gabriel. 
+SELECT b.name FROM friend
+JOIN student a ON a.id = friend.id1
+JOIN student b ON b.id = friend.id2 WHERE a.name = 'Gabriel';

sql/08-query-likes-grade-two-or-more.sql

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+-- For every student who likes someone 2 or more grades younger than themselves, return that student's name and grade, and the name and grade of the student they like. 
+
+SELECT a.name liker_name, a.grade liker_grade, b.name likee_name, b.grade likee_grade
+	FROM student_like
+	JOIN student a ON a.id = student_like.liker_id
+	JOIN student b ON b.id = student_like.likee_id
+	WHERE (a.grade - b.grade) >= 2;

sql/09-mutual-likes.sql

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+-- For every pair of students who both like each other, return the name and grade of both students. Include each pair only once, with the two names in alphabetical order. 
+
+SELECT s1.name liker_name, s1.grade liker_grade, s2.name likee_name, s2.grade likee_grade
+	FROM (
+		SELECT a.liker_id, a.likee_id
+			FROM student_like a
+			JOIN student_like b
+			ON a.liker_id = b.likee_id AND b.liker_id = a.likee_id
+		) mutual
+	JOIN student s1 ON s1.id = mutual.liker_id
+	JOIN student s2 ON s2.id = mutual.likee_id
+	WHERE s1.name < s2.name
+	ORDER BY s1.name ASC;

sql/10-not-liked.sql

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+-- Find all students who do not appear in the like table (as a student who likes or is liked) and return their names and grades. Sort by grade, then by name within each grade. 
+
+SELECT name, grade FROM student
+	WHERE id NOT IN
+		(SELECT likee_id FROM student_like)
+	AND id NOT IN
+		(SELECT liker_id FROM student_like)
+	ORDER BY grade ASC, name ASC;

sql/11-liked-but-does-not-like.sql

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+-- For every situation where student A likes student B, but we have no information about whom B likes (that is, B's id does not appear in the liker_id column of the like table), return A and B's names and grades. 
+
+SELECT a.name, a.grade, b.name, b.grade FROM student_like
+	JOIN student a ON a.id = student_like.liker_id
+	JOIN student b ON b.id = student_like.likee_id
+	WHERE b.id NOT IN (SELECT liker_id FROM student_like);