SQL Exercise: Find the referees managed the number of matches
SQL soccer Database: Joins Exercise-51 with Solution
51. From the following tables, write a SQL query to find the number of matches managed by each referee. Return referee name, country name, number of matches.
Sample table: match_mast
Sample table: referee_mast
Sample table: soccer_country
SELECT c.referee_name, b.country_name, count(a.match_no) 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 c.referee_name, b.country_name;
referee_name | country_name | count -------------------------+----------------+------- Damir Skomina | Slovenia | 4 Martin Atkinson | England | 3 Clement Turpin | France | 2 Jonas Eriksson | Sweden | 3 Ovidiu Hategan | Romania | 2 Sergei Karasev | Russia | 2 Cuneyt Cakir | Turkey | 3 Felix Brych | Germany | 3 Viktor Kassai | Hungary | 3 Carlos Velasco Carballo | Spain | 3 Svein Oddvar Moen | Norway | 2 Milorad Mazic | Serbia | 3 Szymon Marciniak | Poland | 3 Bjorn Kuipers | Netherlands | 3 William Collum | Scotland | 2 Mark Clattenburg | England | 4 Nicola Rizzoli | Italy | 4 Pavel Kralovec | Czech Republic | 2 (18 rows)
The given query in SQL that selects the name of referees, the name of countries, and the count of match numbers in the match_mast table for each combination of referee and 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 referee name and country name using the GROUP BY clause and applies an aggregate function, count(), to count the number of match numbers for each combination of referee and country.
Relational Algebra Expression:
Relational Algebra Tree:
Sample Database: soccer
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Previous SQL Exercise: Identify countries where referees managed most matches.
Next SQL Exercise: Find those referees who managed most of the match.
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