SQL Exercise: Assistant referees of each countries assists matches
46. From the following table, write a SQL query to find the assistant referees of each country assist the number of matches. Sort the result-set in descending order on number of matches. Return country name, number of matches.
Sample table: match_details
match_no | play_stage | team_id | win_lose | decided_by | goal_score | penalty_score | ass_ref | player_gk
----------+------------+---------+----------+------------+------------+---------------+---------+-----------
1 | G | 1207 | W | N | 2 | | 80016 | 160140
1 | G | 1216 | L | N | 1 | | 80020 | 160348
2 | G | 1201 | L | N | 0 | | 80003 | 160001
2 | G | 1221 | W | N | 1 | | 80023 | 160463
3 | G | 1224 | W | N | 2 | | 80031 | 160532
3 | G | 1218 | L | N | 1 | | 80025 | 160392
4 | G | 1206 | D | N | 1 | | 80008 | 160117
4 | G | 1217 | D | N | 1 | | 80019 | 160369
5 | G | 1222 | L | N | 0 | | 80011 | 160486
5 | G | 1204 | W | N | 1 | | 80022 | 160071
6 | G | 1213 | W | N | 1 | | 80036 | 160279
6 | G | 1212 | L | N | 0 | | 80029 | 160256
7 | G | 1208 | W | N | 2 | | 80014 | 160163
7 | G | 1223 | L | N | 0 | | 80006 | 160508
8 | G | 1219 | W | N | 1 | | 80018 | 160416
8 | G | 1205 | L | N | 0 | | 80012 | 160093
9 | G | 1215 | D | N | 1 | | 80017 | 160324
9 | G | 1220 | D | N | 1 | | 80010 | 160439
10 | G | 1203 | L | N | 0 | | 80004 | 160047
10 | G | 1211 | W | N | 2 | | 80007 | 160231
11 | G | 1202 | L | N | 0 | | 80026 | 160024
11 | G | 1209 | W | N | 2 | | 80028 | 160187
12 | G | 1214 | D | N | 1 | | 80009 | 160302
12 | G | 1210 | D | N | 1 | | 80015 | 160208
13 | G | 1217 | L | N | 1 | | 80001 | 160369
13 | G | 1218 | W | N | 2 | | 80002 | 160392
14 | G | 1216 | D | N | 1 | | 80030 | 160348
14 | G | 1221 | D | N | 1 | | 80032 | 160463
15 | G | 1207 | W | N | 2 | | 80033 | 160140
15 | G | 1201 | L | N | 0 | | 80027 | 160001
16 | G | 1206 | W | N | 2 | | 80005 | 160117
16 | G | 1224 | L | N | 1 | | 80013 | 160531
17 | G | 1223 | L | N | 0 | | 80035 | 160508
17 | G | 1212 | W | N | 2 | | 80034 | 160256
18 | G | 1208 | D | N | 0 | | 80021 | 160163
18 | G | 1213 | D | N | 0 | | 80024 | 160278
19 | G | 1211 | W | N | 1 | | 80016 | 160231
19 | G | 1220 | L | N | 0 | | 80020 | 160439
20 | G | 1205 | D | N | 2 | | 80004 | 160093
20 | G | 1204 | D | N | 2 | | 80007 | 160071
21 | G | 1219 | W | N | 3 | | 80017 | 160416
21 | G | 1222 | L | N | 0 | | 80010 | 160486
22 | G | 1203 | W | N | 3 | | 80009 | 160047
22 | G | 1215 | L | N | 0 | | 80015 | 160324
23 | G | 1210 | D | N | 1 | | 80030 | 160208
23 | G | 1209 | D | N | 1 | | 80032 | 160187
24 | G | 1214 | D | N | 0 | | 80008 | 160302
24 | G | 1202 | D | N | 0 | | 80019 | 160024
25 | G | 1216 | L | N | 0 | | 80035 | 160348
25 | G | 1201 | W | N | 1 | | 80034 | 160001
26 | G | 1221 | D | N | 0 | | 80001 | 160463
26 | G | 1207 | D | N | 0 | | 80002 | 160140
27 | G | 1217 | L | N | 0 | | 80011 | 160369
27 | G | 1224 | W | N | 3 | | 80022 | 160531
28 | G | 1218 | D | N | 0 | | 80003 | 160392
28 | G | 1206 | D | N | 0 | | 80023 | 160117
29 | G | 1223 | L | N | 0 | | 80031 | 160508
29 | G | 1213 | W | N | 1 | | 80025 | 160278
30 | G | 1212 | L | N | 0 | | 80026 | 160256
30 | G | 1208 | W | N | 1 | | 80028 | 160163
31 | G | 1205 | L | N | 0 | | 80033 | 160093
31 | G | 1222 | W | N | 2 | | 80027 | 160486
32 | G | 1204 | W | N | 2 | | 80021 | 160071
32 | G | 1219 | L | N | 1 | | 80024 | 160416
33 | G | 1210 | W | N | 2 | | 80018 | 160208
33 | G | 1202 | L | N | 1 | | 80012 | 160024
34 | G | 1209 | D | N | 3 | | 80014 | 160187
34 | G | 1214 | D | N | 3 | | 80006 | 160302
35 | G | 1211 | L | N | 0 | | 80036 | 160233
35 | G | 1215 | W | N | 1 | | 80029 | 160324
36 | G | 1220 | L | N | 0 | | 80005 | 160439
36 | G | 1203 | W | N | 1 | | 80013 | 160047
37 | R | 1221 | L | P | 1 | 4 | 80004 | 160463
37 | R | 1213 | W | P | 1 | 5 | 80007 | 160278
38 | R | 1224 | W | N | 1 | | 80014 | 160531
38 | R | 1212 | L | N | 0 | | 80006 | 160256
39 | R | 1204 | L | N | 0 | | 80003 | 160071
39 | R | 1214 | W | N | 1 | | 80023 | 160302
40 | R | 1207 | W | N | 2 | | 80008 | 160140
40 | R | 1215 | L | N | 1 | | 80019 | 160324
41 | R | 1208 | W | N | 3 | | 80018 | 160163
41 | R | 1218 | L | N | 0 | | 80012 | 160392
42 | R | 1209 | L | N | 0 | | 80017 | 160187
42 | R | 1203 | W | N | 4 | | 80010 | 160047
43 | R | 1211 | W | N | 2 | | 80009 | 160231
43 | R | 1219 | L | N | 0 | | 80015 | 160416
44 | R | 1206 | L | N | 1 | | 80001 | 160117
44 | R | 1210 | W | N | 2 | | 80002 | 160208
45 | Q | 1213 | L | P | 1 | 3 | 80005 | 160278
45 | Q | 1214 | W | P | 1 | 5 | 80013 | 160302
46 | Q | 1224 | W | N | 3 | | 80001 | 160531
46 | Q | 1203 | L | N | 1 | | 80002 | 160047
47 | Q | 1208 | W | P | 1 | 6 | 80016 | 160163
47 | Q | 1211 | L | P | 1 | 5 | 80020 | 160231
48 | Q | 1207 | W | N | 5 | | 80021 | 160140
48 | Q | 1210 | L | N | 2 | | 80024 | 160208
49 | S | 1214 | W | N | 2 | | 80011 | 160302
49 | S | 1224 | L | N | 0 | | 80022 | 160531
50 | S | 1207 | W | N | 2 | | 80008 | 160140
50 | S | 1208 | L | N | 1 | | 80019 | 160163
51 | F | 1214 | W | N | 1 | | 80004 | 160302
51 | F | 1207 | L | N | 0 | | 80007 | 160140
Sample table: asst_referee_mast
ass_ref_id | ass_ref_name | country_id
------------+--------------------------+------------
80034 | Tomas Mokrusch | 1205
80038 | Martin Wilczek | 1205
80004 | Simon Beck | 1206
80006 | Stephen Child | 1206
80007 | Jake Collin | 1206
80014 | Mike Mullarkey | 1206
80026 | Frederic Cano | 1207
80028 | Nicolas Danos | 1207
80005 | Mark Borsch | 1208
80013 | Stefan Lupp | 1208
80016 | Gyorgy Ring | 1209
80020 | Vencel Toth | 1209
80033 | Damien McGraith | 1215
80008 | Elenito Di Liberatore | 1211
80019 | Mauro Tonolini | 1211
80021 | Sander van Roekel | 1226
80024 | Erwin Zeinstra | 1226
80025 | Frank Andas | 1229
80031 | Kim Haglund | 1229
80012 | Tomasz Listkiewicz | 1213
80018 | Pawel Sokolnicki | 1213
80029 | Sebastian Gheorghe | 1216
80036 | Octavian Sovre | 1216
80030 | Nikolay Golubev | 1217
80032 | Tikhon Kalugin | 1217
80037 | Anton Averyanov | 1217
80027 | Frank Connor | 1228
80010 | Dalibor Durdevic | 1227
80017 | Milovan Ristic | 1227
80035 | Roman Slysko | 1218
80001 | Jure Praprotnik | 1225
80002 | Robert Vukan | 1225
80003 | Roberto Alonso Fernandez | 1219
80023 | Juan Yuste Jimenez | 1219
80011 | Mathias Klasenius | 1220
80022 | Daniel Warnmark | 1220
80009 | Bahattin Duran | 1222
80015 | Tarik Ongun | 1222
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
1210 | ISL | Iceland
1211 | ITA | Italy
1212 | NIR | Northern Ireland
1213 | POL | Poland
1214 | POR | Portugal
1215 | IRL | Republic of Ireland
1216 | ROU | Romania
1217 | RUS | Russia
1218 | SVK | Slovakia
1219 | ESP | Spain
1220 | SWE | Sweden
1221 | SUI | Switzerland
1222 | TUR | Turkey
1223 | UKR | Ukraine
1224 | WAL | Wales
1225 | SLO | Slovenia
1226 | NED | Netherlands
1227 | SRB | Serbia
1228 | SCO | Scotland
1229 | NOR | Norway
Sample Solution:
SQL Code:
-- Selecting the country name and the count of distinct match numbers for each country where an assistant referee is involved
SELECT
country_name, -- Selecting the country name from the soccer_country table
COUNT(DISTINCT match_no) -- Counting the distinct match numbers for each country
FROM
match_details a -- Specifying the match_details table with alias 'a'
JOIN
asst_referee_mast c ON a.ass_ref = c.ass_ref_id -- Joining the asst_referee_mast table with match_details based on assistant referee ID
JOIN
soccer_country b ON c.country_id = b.country_id -- Joining the soccer_country table based on country ID
GROUP BY
country_name -- Grouping the results by country name
-- Ordering the results by the count of match numbers in descending order
ORDER BY
COUNT(*) DESC;
Sample Output:
country_name | count
---------------------+-------
England | 7
Slovenia | 4
Italy | 4
Turkey | 3
Hungary | 3
Netherlands | 3
Poland | 3
Germany | 3
Spain | 3
Sweden | 3
Serbia | 3
Russia | 2
France | 2
Norway | 2
Romania | 2
Republic of Ireland | 2
Czech Republic | 2
Scotland | 2
Slovakia | 2
(19 rows)
Code Explanation:
The said query in SQL that returns the number of distinct match_no values for each country in the soccer_country table.
This query is identifies which countries have the most soccer matches with the specified assistant referees.
The JOIN clause joins the match_details, asst_referee_mast, and soccer_country tables using their respective keys (ass_ref in match_details, ass_ref_id in asst_referee_mast, and country_id in soccer_country) to match the data between them.
This orders the results by the count of match_no values in descending order.
Alternative Solutions:
Cross Join with Subquery and HAVING:
-- Selecting the country name and the count of distinct match numbers for each country where an assistant referee is involved
SELECT
b.country_name, -- Selecting the country name from the soccer_country table
COUNT(DISTINCT a.match_no) AS Match_Count -- Counting the distinct match numbers for each country
FROM
soccer_country b -- Specifying the soccer_country table with alias 'b'
CROSS JOIN
asst_referee_mast c -- Performing a cross join with the asst_referee_mast table to get all combinations of country and assistant referee
LEFT JOIN
match_details a ON a.ass_ref = c.ass_ref_id AND c.country_id = b.country_id -- Left joining the match_details table based on assistant referee ID and country ID
GROUP BY
b.country_name -- Grouping the results by country name
HAVING
COUNT(DISTINCT a.match_no) > 0 -- Filtering out countries with no matches involving an assistant referee
-- Ordering the results by the count of match numbers in descending order
ORDER BY
Match_Count DESC;
Explanation:
This query uses a cross join to generate all possible combinations of country_name and ass_ref. It then left joins with match_details to count the distinct matches. The HAVING clause is used to eliminate countries with zero matches.
Correlated Subquery with HAVING:
-- Selecting the country name and the count of distinct match numbers for each country where an assistant referee is involved
SELECT
sub.country_name, -- Selecting the country name from the subquery results
sub.Match_Count -- Selecting the count of distinct match numbers from the subquery results
FROM (
-- Subquery to calculate the count of distinct match numbers for each country
SELECT
b.country_name, -- Selecting the country name from the soccer_country table
(
-- Subquery to count the distinct match numbers where an assistant referee from the current country is involved
SELECT COUNT(DISTINCT a.match_no)
FROM match_details a
JOIN asst_referee_mast c ON a.ass_ref = c.ass_ref_id
WHERE c.country_id = b.country_id -- Filtering matches based on the current country ID
) AS Match_Count -- Assigning the count of distinct match numbers to the alias 'Match_Count'
FROM
soccer_country b -- Specifying the soccer_country table with alias 'b'
) sub -- Assigning the subquery results to the alias 'sub'
WHERE sub.Match_Count > 0 -- Filtering out countries with no matches involving an assistant referee
-- Ordering the results by the count of match numbers in descending order
ORDER BY sub.Match_Count DESC;
Explanation:
This query uses a correlated subquery to count the distinct match_no for each country. The subquery is correlated to the outer query by the country_id and counts the matches accordingly. The HAVING clause is then used to eliminate countries with zero matches.
Relational Algebra Expression:
Relational Algebra Tree:
Practice Online
Sample Database: soccer
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