3v0k4

number_of_runs = # how many times to repeat the check
number_of_threads = # how many concurrent write request
write_url = # url to use for the write requests
write_params = # params to send in each write request
read_url = # url used to check the state of the system after the concurrent write requests

number_of_runs.times do |i|
  puts “run ##{i+1}”
  concurrent_post(number_of_threads, write_url, write_params)
  state = get(read_url)

3v0k4

=> SELECT id, genre, title from films;

 id |  genre   |       title
----+----------+-------------------
  1 | thriller | Blade Runner 2049
  2 | thriller | Inception
  3 | scifi    | Arrival

3v0k4

=> SELECT id, film_id, content FROM reviews;

 id | film_id |                          content
----+---------+-----------------------------------------------------------
  1 |       1 | Visually stunning and thought provoking, but not flawless
  2 |       1 | One of the best sequels of all time
  3 |       1 | Strangely boring, lacking tension and intelligence
  4 |       2 | Amazing Directing, Captivating Plot, Overall Great

3v0k4

=> SELECT genre, count(*) FROM films GROUP BY genre;

  genre   | count
----------+-------
 thriller |     2
 scifi    |     1

3v0k4

=> SELECT title, genre, count(*) FROM films GROUP BY genre;

ERROR:  column "films.title" must appear in the GROUP BY clause or be used in an aggregate function
LINE 1: SELECT title, genre, count(*) FROM films GROUP BY genre;

3v0k4

=> SELECT title, genre, count(*) FROM films GROUP BY title, genre;

       title       |  genre   | count
-------------------+----------+-------
 Blade Runner 2049 | thriller |     1
 Inception         | thriller |     1
 Arrival           | scifi    |     1

3v0k4

=> SELECT string_agg(title, ', ') as titles, genre, count(*) FROM films GROUP BY genre;

            titles            |  genre   | count
------------------------------+----------+-------
 Blade Runner 2049, Inception | thriller |     2
 Arrival                      | scifi    |     1

3v0k4

=> SELECT id, title, genre FROM films GROUP BY id;

 id |       title       |  genre
----+-------------------+----------
  3 | Arrival           | scifi
  1 | Blade Runner 2049 | thriller
  2 | Inception         | thriller

3v0k4

=> SELECT films.id, films.title, films.genre, count(*) as number_of_reviews FROM films LEFT JOIN reviews ON films.id = reviews.film_id GROUP BY films.id;

 id |       title       |  genre   | number_of_reviews
----+-------------------+----------+-------------------
  3 | Arrival           | scifi    |                 1
  1 | Blade Runner 2049 | thriller |                 3
  2 | Inception         | thriller |                 1

3v0k4

=> SELECT films.id, films.title, films.genre, string_agg(reviews.content, E'\n') FROM films LEFT JOIN reviews ON films.id = reviews.film_id GROUP BY films.id;

 id |       title       |  genre   |                        string_agg
----+-------------------+----------+-----------------------------------------------------------
  3 | Arrival           | scifi    |
  1 | Blade Runner 2049 | thriller | Visually stunning and thought provoking, but not flawless+
    |                   |          | One of the best sequels of all time                      +
    |                   |          | Strangely boring, lacking tension and intelligence
  2 | Inception         | thriller | Amazing Directing, Captivating Plot, Overall Great