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SQL Exercise: Find the final four teams in the tournament

SQL soccer Database: Joins Exercise-30 with Solution

30. From the following tables, write a SQL query to find the final four teams in the tournament. Return country name.

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 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 Solution:

SQL Code:

-- This query selects the country names of teams that participated in the 'S' (presumably, group stage) matches.

SELECT 
    country_name -- Selecting the country names of the teams
FROM 
    match_details a -- Specifying the match_details table with an alias 'a'
JOIN 
    soccer_country b ON a.team_id = b.country_id -- Joining the soccer_country table with the match_details table based on the team_id
	-- Filtering matches that are in the 'S' (presumably, group stage)
WHERE 
    play_stage = 'S'; 

Sample Output:

 country_name
--------------
 France
 Germany
 Portugal
 Wales
(4 rows)

Code Explanation:

The said query in SQL that retrieves the country names of teams that have played in the "Semi-Finals" of a soccer tournament.
The JOIN clause joins the 'match_details' table and the 'soccer_country' table using the "team_id" and the "country_id" columns from the respective tables.
The WHERE clause retrieves data for teams that have played in the "Semi-Finals" of a soccer tournament.

Alternative Solutions:

Using EXISTS Clause:

-- This query selects the country names of teams that participated in the 'S' (presumably, group stage) matches.

SELECT 
    country_name -- Selecting the country names of the teams
FROM 
    soccer_country b -- Specifying the soccer_country table with an alias 'b'
WHERE 
    EXISTS ( -- Checking for the existence of at least one record that satisfies the condition within the subquery
        SELECT 1 -- Selecting 1 as a placeholder value (could be any value since we're using EXISTS)
        FROM 
            match_details a -- Specifying the match_details table with an alias 'a' for the subquery
        WHERE 
            a.team_id = b.country_id -- Matching the team ID between the outer query and the subquery
            AND a.play_stage = 'S' -- Filtering matches that are in the 'S' (presumably, group stage)
    );

Explanation:

This query uses the EXISTS clause with a subquery to check if there exists a match in the 'S' play stage for each country in the soccer_country table. If a match is found, the country name is selected.

Using INNER JOIN with Subquery:

-- This query selects the country names of teams that participated in the 'S' (presumably, group stage) matches.

SELECT 
    b.country_name -- Selecting the country names of the teams
FROM 
    soccer_country b -- Specifying the soccer_country table with an alias 'b'
JOIN 
    (
        -- Subquery to select distinct team IDs participating in the group stage matches
        SELECT DISTINCT 
            team_id -- Selecting distinct team IDs from the match_details table
        FROM 
            match_details -- Specifying the match_details table for the subquery
        WHERE 
            play_stage = 'S' -- Filtering matches that are in the 'S' (presumably, group stage)
			-- Joining the main query with the subquery based on the team_id
    ) a ON b.country_id = a.team_id; 

Explanation:

This query first uses a subquery to find distinct team_ids playing in the 'S' play stage. It then joins this subquery with the soccer_country table based on the team_id, resulting in the selection of corresponding country names.

Relational Algebra Expression:

Relational Algebra Expression: Find the final four teams in the tournament.

Relational Algebra Tree:

Relational Algebra Tree: Find the final four teams in the tournament.

Practice Online


Sample Database: soccer

soccer database relationship structure

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