SQL Exercise: Identify countries where referees managed most matches
50. From the following tables, write a SQL query to find the countries from where the referees managed most of the matches. Return country name, number of matches.
Sample table: match_mast
match_no | play_stage | play_date | results | decided_by | goal_score | venue_id | referee_id | audence | plr_of_match | stop1_sec | stop2_sec
----------+------------+------------+---------+------------+------------+----------+------------+---------+--------------+-----------+-----------
1 | G | 2016-06-11 | WIN | N | 2-1 | 20008 | 70007 | 75113 | 160154 | 131 | 242
2 | G | 2016-06-11 | WIN | N | 0-1 | 20002 | 70012 | 33805 | 160476 | 61 | 182
3 | G | 2016-06-11 | WIN | N | 2-1 | 20001 | 70017 | 37831 | 160540 | 64 | 268
4 | G | 2016-06-12 | DRAW | N | 1-1 | 20005 | 70011 | 62343 | 160128 | 0 | 185
5 | G | 2016-06-12 | WIN | N | 0-1 | 20007 | 70006 | 43842 | 160084 | 125 | 325
6 | G | 2016-06-12 | WIN | N | 1-0 | 20006 | 70014 | 33742 | 160291 | 2 | 246
7 | G | 2016-06-13 | WIN | N | 2-0 | 20003 | 70002 | 43035 | 160176 | 89 | 188
8 | G | 2016-06-13 | WIN | N | 1-0 | 20010 | 70009 | 29400 | 160429 | 360 | 182
9 | G | 2016-06-13 | DRAW | N | 1-1 | 20008 | 70010 | 73419 | 160335 | 67 | 194
........
51 | F | 2016-07-11 | WIN | N | 1-0 | 20008 | 70005 | 75868 | 160307 | 161 | 181
Sample table: referee_mast
referee_id | referee_name | country_id
------------+-------------------------+------------
70001 | Damir Skomina | 1225
70002 | Martin Atkinson | 1206
70003 | Felix Brych | 1208
70004 | Cuneyt Cakir | 1222
70005 | Mark Clattenburg | 1206
70006 | Jonas Eriksson | 1220
70007 | Viktor Kassai | 1209
70008 | Bjorn Kuipers | 1226
70009 | Szymon Marciniak | 1213
.......
70018 | Clement Turpin | 1207
Sample table: soccer_country
country_id | country_abbr | country_name
------------+--------------+---------------------
1201 | ALB | Albania
1202 | AUT | Austria
1203 | BEL | Belgium
1204 | CRO | Croatia
1205 | CZE | Czech Republic
1206 | ENG | England
1207 | FRA | France
1208 | GER | Germany
1209 | HUN | Hungary
.......
1229 | NOR | Norway
Sample Solution:
SQL Code:
-- Selecting the country name and the count of matches officiated by referees from each country
SELECT
country_name, -- Selecting the country name
COUNT(match_no) -- Counting the number of matches for each country
FROM
match_mast a -- Specifying the match_mast table with alias 'a'
JOIN
referee_mast c ON a.referee_id = c.referee_id -- Joining the match_mast table with the referee_mast table based on referee ID
JOIN
soccer_country b ON c.country_id = b.country_id -- Joining the referee_mast table with the soccer_country table based on country ID
GROUP BY
country_name -- Grouping the results by country name
HAVING
COUNT(match_no) = (
SELECT
MAX(mm) -- Selecting the maximum count of matches
FROM
(
SELECT
COUNT(match_no) AS mm -- Counting the matches for each country
FROM
match_mast a
JOIN
referee_mast c ON a.referee_id = c.referee_id
JOIN
soccer_country b ON c.country_id = b.country_id
GROUP BY
country_name -- Grouping by country name
) hh -- Subquery alias
);
Sample Output:
country_name | count --------------+------- England | 7 (1 row)
Code Explanation:
The said query in SQL that selects the name of countries and the count of match numbers in the match_mast table for each country.
The JOIN clause in this query then joins the match_mast and referee_mast tables based on the referee_id column and joins the results with soccer_country tables based on the country_id column.
The query groups the results by country name using the GROUP BY clause and applies an aggregate function, count(), to count the number of match numbers for each country. The HAVING clause filters the results to only show the countries whose count of match numbers is equal to the maximum count of match numbers among all countries. The maximum count of match numbers is obtained by a subquery that selects the count of match numbers for each country and then selects the maximum count from those results.
Alternative Solutions:
Using Window Functions:
-- Selecting the country name and the match count for the top-ranked country in terms of the number of matches officiated by referees from each country
SELECT
country_name, -- Selecting the country name
match_count -- Selecting the match count
FROM
(
-- Subquery to calculate the match count and rank for each country
SELECT
b.country_name, -- Selecting the country name
COUNT(a.match_no) AS match_count, -- Counting the number of matches for each country
RANK() OVER (ORDER BY COUNT(a.match_no) DESC) AS rank -- Ranking the countries based on match count in descending order
FROM
match_mast a -- Specifying the match_mast table with alias 'a'
JOIN
referee_mast c ON a.referee_id = c.referee_id -- Joining the match_mast table with the referee_mast table based on referee ID
JOIN
soccer_country b ON c.country_id = b.country_id -- Joining the referee_mast table with the soccer_country table based on country ID
GROUP BY
country_name -- Grouping the results by country name
) ranked -- Alias for the subquery
-- Selecting only the rows where the rank is 1, i.e., the top-ranked country
WHERE
rank = 1;
Explanation:
This query uses a window function RANK() to assign a rank to each country based on the count of matches. It then selects the country with rank 1, which corresponds to the country with the highest match count.
Using JOIN with Subquery:
-- Selecting the country name and the count of matches for each country
SELECT
b.country_name, -- Selecting the country name
COUNT(a.match_no) -- Counting the number of matches for each country
FROM
match_mast a -- Specifying the match_mast table with alias 'a'
JOIN
referee_mast c ON a.referee_id = c.referee_id -- Joining the match_mast table with the referee_mast table based on referee ID
JOIN
soccer_country b ON c.country_id = b.country_id -- Joining the referee_mast table with the soccer_country table based on country ID
JOIN
(
-- Subquery to calculate the maximum match count for each country
SELECT
c.country_id, -- Selecting the country ID
COUNT(a.match_no) AS match_count -- Counting the number of matches for each country
FROM
match_mast a -- Specifying the match_mast table with alias 'a'
JOIN
referee_mast c ON a.referee_id = c.referee_id -- Joining the match_mast table with the referee_mast table based on referee ID
JOIN
soccer_country b ON c.country_id = b.country_id -- Joining the referee_mast table with the soccer_country table based on country ID
GROUP BY
c.country_id -- Grouping the results by country ID
HAVING
COUNT(a.match_no) = (
-- Subquery to find the maximum match count across all countries
SELECT
MAX(match_count) -- Selecting the maximum match count
FROM
(
-- Subquery to calculate the match count for each country
SELECT
COUNT(a.match_no) AS match_count -- Counting the number of matches for each country
FROM
match_mast a -- Specifying the match_mast table with alias 'a'
JOIN
referee_mast c ON a.referee_id = c.referee_id -- Joining the match_mast table with the referee_mast table based on referee ID
JOIN
soccer_country b ON c.country_id = b.country_id -- Joining the referee_mast table with the soccer_country table based on country ID
GROUP BY
c.country_id -- Grouping the results by country ID
) subquery -- Alias for the subquery
)
) max_count ON b.country_id = max_count.country_id -- Joining with the subquery to filter the top-ranked countries
-- Grouping the results by country name
GROUP BY
b.country_name;
Explanation:
This query first calculates the match count for each country using a subquery. It then joins this result with the main query and filters only the rows where the match count matches the maximum match count found in the subquery.
Go to:
PREV : The number of matches each referee has managed.
NEXT : Find the referees managed the number of matches.
Practice Online
Sample Database: soccer
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