SQL exercises on movie Database: Find the reviewer's name and the title of the movie for those reviewers who rated more than one movies

Last update on January 05 2024 12:45:03 (UTC/GMT +8 hours)

SQL movie Database: Subquery Exercise-10 with Solution

10. From the following table, write a SQL query to find movies that have been reviewed by a reviewer and received a rating. Group the result set on reviewer’s name, movie title. Return reviewer’s name, movie title.

Sample table: reviewer

 rev_id |            rev_name
--------+--------------------------------
   9001 | Righty Sock
   9002 | Jack Malvern
   9003 | Flagrant Baronessa
   9004 | Alec Shaw
   9005 |
   9006 | Victor Woeltjen
   9007 | Simon Wright
   9008 | Neal Wruck
   9009 | Paul Monks
   9010 | Mike Salvati
   9011 |
   9012 | Wesley S. Walker
   9013 | Sasha Goldshtein
   9014 | Josh Cates
   9015 | Krug Stillo
   9016 | Scott LeBrun
   9017 | Hannah Steele
   9018 | Vincent Cadena
   9019 | Brandt Sponseller
   9020 | Richard Adams

Sample table: rating

 mov_id | rev_id | rev_stars | num_o_ratings
--------+--------+-----------+---------------
    901 |   9001 |      8.40 |        263575
    902 |   9002 |      7.90 |         20207
    903 |   9003 |      8.30 |        202778
    906 |   9005 |      8.20 |        484746
    924 |   9006 |      7.30 |
    908 |   9007 |      8.60 |        779489
    909 |   9008 |           |        227235
    910 |   9009 |      3.00 |        195961
    911 |   9010 |      8.10 |        203875
    912 |   9011 |      8.40 |
    914 |   9013 |      7.00 |        862618
    915 |   9001 |      7.70 |        830095
    916 |   9014 |      4.00 |        642132
    925 |   9015 |      7.70 |         81328
    918 |   9016 |           |        580301
    920 |   9017 |      8.10 |        609451
    921 |   9018 |      8.00 |        667758
    922 |   9019 |      8.40 |        511613
    923 |   9020 |      6.70 |         13091

Sample table: movie

 mov_id |                     mov_title                      | mov_year | mov_time |    mov_lang     | mov_dt_rel | mov_rel_country
--------+----------------------------------------------------+----------+----------+-----------------+------------+-----------------
    901 | Vertigo                                            |     1958 |      128 | English         | 1958-08-24 | UK
    902 | The Innocents                                      |     1961 |      100 | English         | 1962-02-19 | SW
    903 | Lawrence of Arabia                                 |     1962 |      216 | English         | 1962-12-11 | UK
    904 | The Deer Hunter                                    |     1978 |      183 | English         | 1979-03-08 | UK
    905 | Amadeus                                            |     1984 |      160 | English         | 1985-01-07 | UK
    906 | Blade Runner                                       |     1982 |      117 | English         | 1982-09-09 | UK
    907 | Eyes Wide Shut                                     |     1999 |      159 | English         |            | UK
    908 | The Usual Suspects                                 |     1995 |      106 | English         | 1995-08-25 | UK
    909 | Chinatown                                          |     1974 |      130 | English         | 1974-08-09 | UK
    910 | Boogie Nights                                      |     1997 |      155 | English         | 1998-02-16 | UK
    911 | Annie Hall                                         |     1977 |       93 | English         | 1977-04-20 | USA
    912 | Princess Mononoke                                  |     1997 |      134 | Japanese        | 2001-10-19 | UK
    913 | The Shawshank Redemption                           |     1994 |      142 | English         | 1995-02-17 | UK
    914 | American Beauty                                    |     1999 |      122 | English         |            | UK
    915 | Titanic                                            |     1997 |      194 | English         | 1998-01-23 | UK
    916 | Good Will Hunting                                  |     1997 |      126 | English         | 1998-06-03 | UK
    917 | Deliverance                                        |     1972 |      109 | English         | 1982-10-05 | UK
    918 | Trainspotting                                      |     1996 |       94 | English         | 1996-02-23 | UK
    919 | The Prestige                                       |     2006 |      130 | English         | 2006-11-10 | UK
    920 | Donnie Darko                                       |     2001 |      113 | English         |            | UK
    921 | Slumdog Millionaire                                |     2008 |      120 | English         | 2009-01-09 | UK
    922 | Aliens                                             |     1986 |      137 | English         | 1986-08-29 | UK
    923 | Beyond the Sea                                     |     2004 |      118 | English         | 2004-11-26 | UK
    924 | Avatar                                             |     2009 |      162 | English         | 2009-12-17 | UK
    926 | Seven Samurai                                      |     1954 |      207 | Japanese        | 1954-04-26 | JP
    927 | Spirited Away                                      |     2001 |      125 | Japanese        | 2003-09-12 | UK
    928 | Back to the Future                                 |     1985 |      116 | English         | 1985-12-04 | UK
    925 | Braveheart                                         |     1995 |      178 | English         | 1995-09-08 | UK

Sample Solution:

-- Selecting reviewer name and movie title
-- Using the 'reviewer', 'movie', 'rating', and 'rating r2' tables
-- Joining tables based on mov_id and rev_id
SELECT rev_name, mov_title 
FROM reviewer, movie, rating, rating r2
WHERE rating.mov_id = movie.mov_id 
  AND reviewer.rev_id = rating.rev_ID 
  AND rating.rev_id = r2.rev_id 
-- Grouping the result set by rev_name and mov_title
GROUP BY rev_name, mov_title 
-- Filtering out groups where the count of entries is not greater than 1
HAVING count(*) > 1;

Sample Output:

            rev_name            |                     mov_title
--------------------------------+----------------------------------------------------
 Righty Sock                    | Titanic
 Righty Sock                    | Vertigo
(2 rows)

Code Explanation:

The given statement in SQL that selects the names of reviewers and the titles of movies that they have reviewed more than once, by joining the reviewer, movie, and rating tables, grouping the results by reviewer and movie, and filtering the results to only show combinations where the reviewer has reviewed the movie more than once.
The conditions specifies for joining that the mov_id column in the rating table and movie table must match, the rev_id column in the reviewer table and the rating table must match, and the rev_id column in the rating table must also match the rev_id column in the r2 table which is the alias of rating table.
The results are group by the rev_name and mov_title, and then applies a HAVING clause that filters the results to only show combinations where the count of rows in the group (i.e. the number of times the reviewer has reviewed the movie) is greater than 1.

Alternative Solution:

Using INNER JOIN:


SELECT r1.rev_name, m.mov_title
FROM reviewer r1
INNER JOIN rating ON r1.rev_id = rating.rev_id
INNER JOIN movie m ON rating.mov_id = m.mov_id
INNER JOIN rating r2 ON rating.rev_id = r2.rev_id
GROUP BY r1.rev_name, m.mov_title
HAVING COUNT(*) > 1;

Explanation:

This query uses INNER JOINs to combine the reviewer, rating, and movie tables based on their respective IDs. It then groups the result by rev_name and mov_title and applies a HAVING clause to filter for rows where the count is greater than 1.

Relational Algebra Expression: