SQL Exercise: The number of matches each referee has managed

SQL soccer Database: Joins Exercise-49 with Solution

49. From the following tables, write a SQL query to count the number of matches managed by referees of each country. Return country name, number of matches.

Sample table: match_mast

Sample table: referee_mast

Sample table: soccer_country

Sample Solution:

SQL Code:

SELECT country_name,
       count(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 country_name
ORDER BY count(match_no) DESC;

Sample Output:

  country_name  | count
----------------+-------
 England        |     7
 Italy          |     4
 Slovenia       |     4
 Spain          |     3
 Serbia         |     3
 Netherlands    |     3
 Turkey         |     3
 Germany        |     3
 Poland         |     3
 Sweden         |     3
 Hungary        |     3
 France         |     2
 Czech Republic |     2
 Norway         |     2
 Russia         |     2
 Romania        |     2
 Scotland       |     2
(17 rows)

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 results are then ordered in descending order of the count of match numbers using the ORDER BY clause.

Relational Algebra Expression:

Relational Algebra Tree:

Practice Online

Sample Database: soccer

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Previous SQL Exercise: List the referees with their countries for each match.
Next SQL Exercise: Identify countries where referees managed most matches.