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Formatted question description: https://leetcode.ca/all/1783.html
1783. Grand Slam Titles
Level
Medium
Description
Table: Players
+----------------+---------+
| Column Name | Type |
+----------------+---------+
| player_id | int |
| player_name | varchar |
+----------------+---------+
player_id is the primary key for this table.
Each row in this table contains the name and the ID of a tennis player.
Table: Championships
+---------------+---------+
| Column Name | Type |
+---------------+---------+
| year | int |
| Wimbledon | int |
| Fr_open | int |
| US_open | int |
| Au_open | int |
+---------------+---------+
year is the primary key for this table.
Each row of this table containts the IDs of the players who won one each tennis tournament of the grand slam.
Write an SQL query to report the number of grand slam tournaments won by each player. Do not include the players who did not win any tournament.
Return the result table in any order.
The query result format is in the following example:
Players table:
+-----------+-------------+
| player_id | player_name |
+-----------+-------------+
| 1 | Nadal |
| 2 | Federer |
| 3 | Novak |
+-----------+-------------+
Championships table:
+------+-----------+---------+---------+---------+
| year | Wimbledon | Fr_open | US_open | Au_open |
+------+-----------+---------+---------+---------+
| 2018 | 1 | 1 | 1 | 1 |
| 2019 | 1 | 1 | 2 | 2 |
| 2020 | 2 | 1 | 2 | 2 |
+------+-----------+---------+---------+---------+
Result table:
+-----------+-------------+-------------------+
| player_id | player_name | grand_slams_count |
+-----------+-------------+-------------------+
| 2 | Federer | 5 |
| 1 | Nadal | 7 |
+-----------+-------------+-------------------+
Player 1 (Nadal) won 7 titles: Wimbledon (2018, 2019), Fr_open (2018, 2019, 2020), US_open (2018), and Au_open (2018).
Player 2 (Federer) won 5 titles: Wimbledon (2020), US_open (2019, 2020), and Au_open (2019, 2020).
Player 3 (Novak) did not win anything, we did not include them in the result table.
Solution
Use union all to join the four tournaments. Use inner join to join the entries. Finally, group the result by player_id.
# Write your MySQL query statement below
select p.player_id, player_name, count(*) as grand_slams_count
from Players p inner join (
select Wimbledon as player_id from Championships union all
select Fr_open from Championships union all
select US_open from Championships union all
select Au_open from Championships
) t
on p.player_id = t.player_id
group by p.player_id;