SQL Exercise: Find the number of captains who were also goalkeepers

SQL soccer Database: Joins Exercise-40 with Solution

40. From the following tables, write a SQL query to find the number of captains who was also the goalkeeper. Return number of captains.

Sample table: match_captain

Sample table: player_mast

Sample table: soccer_country

Sample Solution:

SQL Code:

SELECT count(DISTINCT player_name)
FROM match_captain a
JOIN soccer_country b ON a.team_id=b.country_id
JOIN player_mast c ON a.player_captain=c.player_id
AND posi_to_play='GK';

Sample Output:

 count
-------
     4
(1 row)

Code Explanation:

The said query in SQL that retrieves the number of distinct player names who have played as goalkeepers and acted as captains in matches for their respective countries.
The JOIN clause joins the tables match_captain and the soccer_country based on the columns team_id and country_id and join the player_mast with the result set based on the player_captain column of match_captain table and player_id column of player_mast table.
The WHERE clause filters the results to only include players who have played in the goalkeeper position.

Relational Algebra Expression:

Relational Algebra Tree:

Practice Online

Sample Database: soccer

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