Mock Sql3 Solutions

market-analysis-ii.sql

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+"""
+
+Table: Users
++----------------+---------+
+| Column Name    | Type    |
++----------------+---------+
+| user_id        | int     |
+| join_date      | date    |
+| favorite_brand | varchar |
++----------------+---------+
+user_id is the primary key (column with unique values) of this table.
+This table has the info of the users of an online shopping website where users can sell and buy items.
+
+Table: Orders
++---------------+---------+
+| Column Name   | Type    |
++---------------+---------+
+| order_id      | int     |
+| order_date    | date    |
+| item_id       | int     |
+| buyer_id      | int     |
+| seller_id     | int     |
++---------------+---------+
+order_id is the primary key (column with unique values) of this table.
+item_id is a foreign key (reference column) to the Items table.
+buyer_id and seller_id are foreign keys to the Users table.
+
+Table: Items
++---------------+---------+
+| Column Name   | Type    |
++---------------+---------+
+| item_id       | int     |
+| item_brand    | varchar |
++---------------+---------+
+item_id is the primary key (column with unique values) of this table.
+
+
+Write a solution to find for each user whether the brand of the second item (by date) they sold is their favorite brand. 
+If a user sold less than two items, report the answer for that user as no. It is guaranteed that no seller sells more than one item in a day.
+
+Return the result table in any order.
+
+The result format is in the following example.
+
+Input: 
+Users table:
++---------+------------+----------------+
+| user_id | join_date  | favorite_brand |
++---------+------------+----------------+
+| 1       | 2019-01-01 | Lenovo         |
+| 2       | 2019-02-09 | Samsung        |
+| 3       | 2019-01-19 | LG             |
+| 4       | 2019-05-21 | HP             |
++---------+------------+----------------+
+Orders table:
++----------+------------+---------+----------+-----------+
+| order_id | order_date | item_id | buyer_id | seller_id |
++----------+------------+---------+----------+-----------+
+| 1        | 2019-08-01 | 4       | 1        | 2         |
+| 2        | 2019-08-02 | 2       | 1        | 3         |
+| 3        | 2019-08-03 | 3       | 2        | 3         |
+| 4        | 2019-08-04 | 1       | 4        | 2         |
+| 5        | 2019-08-04 | 1       | 3        | 4         |
+| 6        | 2019-08-05 | 2       | 2        | 4         |
++----------+------------+---------+----------+-----------+
+Items table:
++---------+------------+
+| item_id | item_brand |
++---------+------------+
+| 1       | Samsung    |
+| 2       | Lenovo     |
+| 3       | LG         |
+| 4       | HP         |
++---------+------------+
+Output: 
++-----------+--------------------+
+| seller_id | 2nd_item_fav_brand |
++-----------+--------------------+
+| 1         | no                 |
+| 2         | yes                |
+| 3         | yes                |
+| 4         | no                 |
++-----------+--------------------+
+
+"""
+
+with cte as(
+  select 
+    *, 
+    rank() over(partition by seller_id order by order_date) as rnk
+  from 
+    orders 
+),
+cte2 as (
+  select 
+    seller_id, i.item_id, rnk, i.item_brand
+  from 
+    cte c join items i
+  on 
+    c.item_id = i.item_id
+  where 
+    rnk = 2
+)
+select 
+  u.user_id as seller_id,
+case
+    when favorite_brand = item_brand then "yes"
+    else "no"
+    end as 2nd_item_fav_brand
+from 
+  users u left join cte2 c
+on 
+  u.user_id = c.seller_id

tournament-winners.sql

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+"""
+
+Table: Players
++-------------+-------+
+| Column Name | Type  |
++-------------+-------+
+| player_id   | int   |
+| group_id    | int   |
++-------------+-------+
+player_id is the primary key (column with unique values) of this table.
+Each row of this table indicates the group of each player.
+
+Table: Matches
++---------------+---------+
+| Column Name   | Type    |
++---------------+---------+
+| match_id      | int     |
+| first_player  | int     |
+| second_player | int     | 
+| first_score   | int     |
+| second_score  | int     |
++---------------+---------+
+match_id is the primary key (column with unique values) of this table.
+Each row is a record of a match, first_player and second_player contain the player_id of each match.
+first_score and second_score contain the number of points of the first_player and second_player respectively.
+You may assume that, in each match, players belong to the same group.
+
+The winner in each group is the player who scored the maximum total points within the group. In the case of a tie, the lowest player_id wins.
+
+Write a solution to find the winner in each group.
+
+Return the result table in any order.
+
+The result format is in the following example.
+
+Input: 
+Players table:
++-----------+------------+
+| player_id | group_id   |
++-----------+------------+
+| 15        | 1          |
+| 25        | 1          |
+| 30        | 1          |
+| 45        | 1          |
+| 10        | 2          |
+| 35        | 2          |
+| 50        | 2          |
+| 20        | 3          |
+| 40        | 3          |
++-----------+------------+
+Matches table:
++------------+--------------+---------------+-------------+--------------+
+| match_id   | first_player | second_player | first_score | second_score |
++------------+--------------+---------------+-------------+--------------+
+| 1          | 15           | 45            | 3           | 0            |
+| 2          | 30           | 25            | 1           | 2            |
+| 3          | 30           | 15            | 2           | 0            |
+| 4          | 40           | 20            | 5           | 2            |
+| 5          | 35           | 50            | 1           | 1            |
++------------+--------------+---------------+-------------+--------------+
+Output: 
++-----------+------------+
+| group_id  | player_id  |
++-----------+------------+ 
+| 1         | 15         |
+| 2         | 35         |
+| 3         | 40         |
++-----------+------------+
+
+"""
+
+with cte as(
+  select 
+    first_player as player, 
+    first_score as score 
+  from 
+    Matches 
+  union all
+  select 
+    second_player as player, 
+    second_score as score
+  from 
+    Matches 
+),
+cte2 as(
+  select 
+    player, 
+    sum(score) as total
+  from 
+    cte 
+  group by 
+    player
+)
+
+select
+  distinct group_id,
+  first_value(c.player) over(partition by group_id order by total desc, p.player_id) as player_id
+from 
+    cte2 as c join players p
+on 
+  c.player = p.player_id