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LeetCode 코딩 테스트 - Find Students Who Improved(LV.Medium)

Table: Scores+-------------+---------+| Column Name | Type |+-------------+---------+| student_id | int || subject | varchar || score | int || exam_date | varchar |+-------------+---------+(student_id, subject, exam_date) is the primary key for this table.Each row contains information about a student's score in a specific subject on a particular exam date. score is betwee..

Table: transactions+------------------+------+| Column Name | Type | +------------------+------+| transaction_id | int || amount | int || transaction_date | date |+------------------+------+The transactions_id column uniquely identifies each row in this table.Each row of this table contains the transaction id, amount and transaction date.Write a solution to find the sum of amo..

Table: UserActivity+------------------+---------+| Column Name | Type | +------------------+---------+| user_id | int || activity_date | date || activity_type | varchar || activity_duration| int |+------------------+---------+(user_id, activity_date, activity_type) is the unique key for this table.activity_type is one of ('free_trial', 'paid', 'cancelled').activ..

Table: Samples+----------------+---------+| Column Name | Type | +----------------+---------+| sample_id | int || dna_sequence | varchar || species | varchar |+----------------+---------+sample_id is the unique key for this table.Each row contains a DNA sequence represented as a string of characters (A, T, G, C) and the species it was collected from.Biologists are studyin..

Table: Signups+----------------+----------+| Column Name | Type |+----------------+----------+| user_id | int || time_stamp | datetime |+----------------+----------+user_id is the column of unique values for this table.Each row contains information about the signup time for the user with ID user_id. Table: Confirmations+----------------+----------+| Column Name | Type ..

Table: Accounts+-------------+------+| Column Name | Type |+-------------+------+| account_id | int || income | int |+-------------+------+account_id is the primary key (column with unique values) for this table.Each row contains information about the monthly income for one bank account. Write a solution to calculate the number of bank accounts for each salary category. The salary catego..

Table: Employee+-------------+------+| Column Name | Type |+-------------+------+| id | int || salary | int |+-------------+------+id is the primary key (column with unique values) for this table.Each row of this table contains information about the salary of an employee. Write a solution to find the nth highest salary from the Employee table. If there is no nth highest salary, r..

Table: Activity+--------------+---------+| Column Name | Type |+--------------+---------+| player_id | int || device_id | int || event_date | date || games_played | int |+--------------+---------+(player_id, event_date) is the primary key (combination of columns with unique values) of this table.This table shows the activity of players of some games.Each row is a recor..

Table: Movies+---------------+---------+| Column Name | Type |+---------------+---------+| movie_id | int || title | varchar |+---------------+---------+movie_id is the primary key (column with unique values) for this table.title is the name of the movie. Table: Users+---------------+---------+| Column Name | Type |+---------------+---------+| user_id | int |..

Table: Employee+-------------+------+| Column Name | Type |+-------------+------+| id | int || salary | int |+-------------+------+id is the primary key (column with unique values) for this table.Each row of this table contains information about the salary of an employee. Write a solution to find the second highest distinct salary from the Employee table. If there is no second hi..