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leetcode/problem/average-selling-price.html Normal file
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<p>Table: <code>Prices</code></p>
<pre>
+---------------+---------+
| Column Name | Type |
+---------------+---------+
| product_id | int |
| start_date | date |
| end_date | date |
| price | int |
+---------------+---------+
(product_id, start_date, end_date) is the primary key (combination of columns with unique values) for this table.
Each row of this table indicates the price of the product_id in the period from start_date to end_date.
For each product_id there will be no two overlapping periods. That means there will be no two intersecting periods for the same product_id.
</pre>
<p>&nbsp;</p>
<p>Table: <code>UnitsSold</code></p>
<pre>
+---------------+---------+
| Column Name | Type |
+---------------+---------+
| product_id | int |
| purchase_date | date |
| units | int |
+---------------+---------+
This table may contain duplicate rows.
Each row of this table indicates the date, units, and product_id of each product sold.
</pre>
<p>&nbsp;</p>
<p>Write a solution to find the average selling price for each product. <code>average_price</code> should be <strong>rounded to 2 decimal places</strong>.</p>
<p>Return the result table in <strong>any order</strong>.</p>
<p>The&nbsp;result format is in the following example.</p>
<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<pre>
<strong>Input:</strong>
Prices table:
+------------+------------+------------+--------+
| product_id | start_date | end_date | price |
+------------+------------+------------+--------+
| 1 | 2019-02-17 | 2019-02-28 | 5 |
| 1 | 2019-03-01 | 2019-03-22 | 20 |
| 2 | 2019-02-01 | 2019-02-20 | 15 |
| 2 | 2019-02-21 | 2019-03-31 | 30 |
+------------+------------+------------+--------+
UnitsSold table:
+------------+---------------+-------+
| product_id | purchase_date | units |
+------------+---------------+-------+
| 1 | 2019-02-25 | 100 |
| 1 | 2019-03-01 | 15 |
| 2 | 2019-02-10 | 200 |
| 2 | 2019-03-22 | 30 |
+------------+---------------+-------+
<strong>Output:</strong>
+------------+---------------+
| product_id | average_price |
+------------+---------------+
| 1 | 6.96 |
| 2 | 16.96 |
+------------+---------------+
<strong>Explanation:</strong>
Average selling price = Total Price of Product / Number of products sold.
Average selling price for product 1 = ((100 * 5) + (15 * 20)) / 115 = 6.96
Average selling price for product 2 = ((200 * 15) + (30 * 30)) / 230 = 16.96
</pre>

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leetcode/problem/average-time-of-process-per-machine.html Normal file
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<p>Table: <code>Activity</code></p>
<pre>
+----------------+---------+
| Column Name | Type |
+----------------+---------+
| machine_id | int |
| process_id | int |
| activity_type | enum |
| timestamp | float |
+----------------+---------+
The table shows the user activities for a factory website.
(machine_id, process_id, activity_type) is the primary key (combination of columns with unique values) of this table.
machine_id is the ID of a machine.
process_id is the ID of a process running on the machine with ID machine_id.
activity_type is an ENUM (category) of type (&#39;start&#39;, &#39;end&#39;).
timestamp is a float representing the current time in seconds.
&#39;start&#39; means the machine starts the process at the given timestamp and &#39;end&#39; means the machine ends the process at the given timestamp.
The &#39;start&#39; timestamp will always be before the &#39;end&#39; timestamp for every (machine_id, process_id) pair.</pre>
<p>&nbsp;</p>
<p>There is a factory website that has several machines each running the <strong>same number of processes</strong>. Write a solution&nbsp;to find the <strong>average time</strong> each machine takes to complete a process.</p>
<p>The time to complete a process is the <code>&#39;end&#39; timestamp</code> minus the <code>&#39;start&#39; timestamp</code>. The average time is calculated by the total time to complete every process on the machine divided by the number of processes that were run.</p>
<p>The resulting table should have the <code>machine_id</code> along with the <strong>average time</strong> as <code>processing_time</code>, which should be <strong>rounded to 3 decimal places</strong>.</p>
<p>Return the result table in <strong>any order</strong>.</p>
<p>The result format is in the following example.</p>
<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<pre>
<strong>Input:</strong>
Activity table:
+------------+------------+---------------+-----------+
| machine_id | process_id | activity_type | timestamp |
+------------+------------+---------------+-----------+
| 0 | 0 | start | 0.712 |
| 0 | 0 | end | 1.520 |
| 0 | 1 | start | 3.140 |
| 0 | 1 | end | 4.120 |
| 1 | 0 | start | 0.550 |
| 1 | 0 | end | 1.550 |
| 1 | 1 | start | 0.430 |
| 1 | 1 | end | 1.420 |
| 2 | 0 | start | 4.100 |
| 2 | 0 | end | 4.512 |
| 2 | 1 | start | 2.500 |
| 2 | 1 | end | 5.000 |
+------------+------------+---------------+-----------+
<strong>Output:</strong>
+------------+-----------------+
| machine_id | processing_time |
+------------+-----------------+
| 0 | 0.894 |
| 1 | 0.995 |
| 2 | 1.456 |
+------------+-----------------+
<strong>Explanation:</strong>
There are 3 machines running 2 processes each.
Machine 0&#39;s average time is ((1.520 - 0.712) + (4.120 - 3.140)) / 2 = 0.894
Machine 1&#39;s average time is ((1.550 - 0.550) + (1.420 - 0.430)) / 2 = 0.995
Machine 2&#39;s average time is ((4.512 - 4.100) + (5.000 - 2.500)) / 2 = 1.456
</pre>

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<p>Table: <code>MyNumbers</code></p>
<pre>
+-------------+------+
| Column Name | Type |
+-------------+------+
| num | int |
+-------------+------+
This table may contain duplicates (In other words, there is no primary key for this table in SQL).
Each row of this table contains an integer.
</pre>
<p>&nbsp;</p>
<p>A <strong>single number</strong> is a number that appeared only once in the <code>MyNumbers</code> table.</p>
<p>Find the largest <strong>single number</strong>. If there is no <strong>single number</strong>, report <code>null</code>.</p>
<p>The result format is in the following example.</p>
<ptable> </ptable>
<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<pre>
<strong>Input:</strong>
MyNumbers table:
+-----+
| num |
+-----+
| 8 |
| 8 |
| 3 |
| 3 |
| 1 |
| 4 |
| 5 |
| 6 |
+-----+
<strong>Output:</strong>
+-----+
| num |
+-----+
| 6 |
+-----+
<strong>Explanation:</strong> The single numbers are 1, 4, 5, and 6.
Since 6 is the largest single number, we return it.
</pre>
<p><strong class="example">Example 2:</strong></p>
<pre>
<strong>Input:</strong>
MyNumbers table:
+-----+
| num |
+-----+
| 8 |
| 8 |
| 7 |
| 7 |
| 3 |
| 3 |
| 3 |
+-----+
<strong>Output:</strong>
+------+
| num |
+------+
| null |
+------+
<strong>Explanation:</strong> There are no single numbers in the input table so we return null.
</pre>

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<p>Table: <code>Signups</code></p>
<pre>
+----------------+----------+
| 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.
</pre>
<p>&nbsp;</p>
<p>Table: <code>Confirmations</code></p>
<pre>
+----------------+----------+
| Column Name | Type |
+----------------+----------+
| user_id | int |
| time_stamp | datetime |
| action | ENUM |
+----------------+----------+
(user_id, time_stamp) is the primary key (combination of columns with unique values) for this table.
user_id is a foreign key (reference column) to the Signups table.
action is an ENUM (category) of the type (&#39;confirmed&#39;, &#39;timeout&#39;)
Each row of this table indicates that the user with ID user_id requested a confirmation message at time_stamp and that confirmation message was either confirmed (&#39;confirmed&#39;) or expired without confirming (&#39;timeout&#39;).
</pre>
<p>&nbsp;</p>
<p>The <strong>confirmation rate</strong> of a user is the number of <code>&#39;confirmed&#39;</code> messages divided by the total number of requested confirmation messages. The confirmation rate of a user that did not request any confirmation messages is <code>0</code>. Round the confirmation rate to <strong>two decimal</strong> places.</p>
<p>Write a solution to find the <strong>confirmation rate</strong> of each user.</p>
<p>Return the result table in <strong>any order</strong>.</p>
<p>The result format is in the following example.</p>
<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<pre>
<strong>Input:</strong>
Signups table:
+---------+---------------------+
| user_id | time_stamp |
+---------+---------------------+
| 3 | 2020-03-21 10:16:13 |
| 7 | 2020-01-04 13:57:59 |
| 2 | 2020-07-29 23:09:44 |
| 6 | 2020-12-09 10:39:37 |
+---------+---------------------+
Confirmations table:
+---------+---------------------+-----------+
| user_id | time_stamp | action |
+---------+---------------------+-----------+
| 3 | 2021-01-06 03:30:46 | timeout |
| 3 | 2021-07-14 14:00:00 | timeout |
| 7 | 2021-06-12 11:57:29 | confirmed |
| 7 | 2021-06-13 12:58:28 | confirmed |
| 7 | 2021-06-14 13:59:27 | confirmed |
| 2 | 2021-01-22 00:00:00 | confirmed |
| 2 | 2021-02-28 23:59:59 | timeout |
+---------+---------------------+-----------+
<strong>Output:</strong>
+---------+-------------------+
| user_id | confirmation_rate |
+---------+-------------------+
| 6 | 0.00 |
| 3 | 0.00 |
| 7 | 1.00 |
| 2 | 0.50 |
+---------+-------------------+
<strong>Explanation:</strong>
User 6 did not request any confirmation messages. The confirmation rate is 0.
User 3 made 2 requests and both timed out. The confirmation rate is 0.
User 7 made 3 requests and all were confirmed. The confirmation rate is 1.
User 2 made 2 requests where one was confirmed and the other timed out. The confirmation rate is 1 / 2 = 0.5.
</pre>

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<p>Table: <code>Accounts</code></p>
<pre>
+-------------+------+
| 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.
</pre>
<p>&nbsp;</p>
<p>Write a solution&nbsp;to calculate the number of bank accounts for each salary category. The salary categories are:</p>
<ul>
<li><code>&quot;Low Salary&quot;</code>: All the salaries <strong>strictly less</strong> than <code>$20000</code>.</li>
<li><code>&quot;Average Salary&quot;</code>: All the salaries in the <strong>inclusive</strong> range <code>[$20000, $50000]</code>.</li>
<li><code>&quot;High Salary&quot;</code>: All the salaries <strong>strictly greater</strong> than <code>$50000</code>.</li>
</ul>
<p>The result table <strong>must</strong> contain all three categories. If there are no accounts in a category,&nbsp;return&nbsp;<code>0</code>.</p>
<p>Return the result table in <strong>any order</strong>.</p>
<p>The&nbsp;result format is in the following example.</p>
<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<pre>
<strong>Input:</strong>
Accounts table:
+------------+--------+
| account_id | income |
+------------+--------+
| 3 | 108939 |
| 2 | 12747 |
| 8 | 87709 |
| 6 | 91796 |
+------------+--------+
<strong>Output:</strong>
+----------------+----------------+
| category | accounts_count |
+----------------+----------------+
| Low Salary | 1 |
| Average Salary | 0 |
| High Salary | 3 |
+----------------+----------------+
<strong>Explanation:</strong>
Low Salary: Account 2.
Average Salary: No accounts.
High Salary: Accounts 3, 6, and 8.
</pre>

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<p>Table: <code>Customer</code></p>
<pre>
+-------------+---------+
| Column Name | Type |
+-------------+---------+
| customer_id | int |
| product_key | int |
+-------------+---------+
This table may contain duplicates rows.
<code>customer_id</code> is not NULL<code>.</code>
product_key is a foreign key (reference column) to <code>Product</code> table.
</pre>
<p>&nbsp;</p>
<p>Table: <code>Product</code></p>
<pre>
+-------------+---------+
| Column Name | Type |
+-------------+---------+
| product_key | int |
+-------------+---------+
product_key is the primary key (column with unique values) for this table.
</pre>
<p>&nbsp;</p>
<p>Write a solution to report the customer ids from the <code>Customer</code> table that bought all the products in the <code>Product</code> table.</p>
<p>Return the result table in <strong>any order</strong>.</p>
<p>The&nbsp;result format is in the following example.</p>
<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<pre>
<strong>Input:</strong>
Customer table:
+-------------+-------------+
| customer_id | product_key |
+-------------+-------------+
| 1 | 5 |
| 2 | 6 |
| 3 | 5 |
| 3 | 6 |
| 1 | 6 |
+-------------+-------------+
Product table:
+-------------+
| product_key |
+-------------+
| 5 |
| 6 |
+-------------+
<strong>Output:</strong>
+-------------+
| customer_id |
+-------------+
| 1 |
| 3 |
+-------------+
<strong>Explanation:</strong>
The customers who bought all the products (5 and 6) are customers with IDs 1 and 3.
</pre>

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<p>Table: <code>Employee</code></p>
<pre>
+-------------+---------+
| Column Name | Type |
+-------------+---------+
| empId | int |
| name | varchar |
| supervisor | int |
| salary | int |
+-------------+---------+
empId is the column with unique values for this table.
Each row of this table indicates the name and the ID of an employee in addition to their salary and the id of their manager.
</pre>
<p>&nbsp;</p>
<p>Table: <code>Bonus</code></p>
<pre>
+-------------+------+
| Column Name | Type |
+-------------+------+
| empId | int |
| bonus | int |
+-------------+------+
empId is the column of unique values for this table.
empId is a foreign key (reference column) to empId from the Employee table.
Each row of this table contains the id of an employee and their respective bonus.
</pre>
<p>&nbsp;</p>
<p>Write a solution to report the name and bonus amount of each employee with a bonus <strong>less than</strong> <code>1000</code>.</p>
<p>Return the result table in <strong>any order</strong>.</p>
<p>The&nbsp;result format is in the following example.</p>
<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<pre>
<strong>Input:</strong>
Employee table:
+-------+--------+------------+--------+
| empId | name | supervisor | salary |
+-------+--------+------------+--------+
| 3 | Brad | null | 4000 |
| 1 | John | 3 | 1000 |
| 2 | Dan | 3 | 2000 |
| 4 | Thomas | 3 | 4000 |
+-------+--------+------------+--------+
Bonus table:
+-------+-------+
| empId | bonus |
+-------+-------+
| 2 | 500 |
| 4 | 2000 |
+-------+-------+
<strong>Output:</strong>
+------+-------+
| name | bonus |
+------+-------+
| Brad | null |
| John | null |
| Dan | 500 |
+------+-------+
</pre>

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<p>Table: <code>Employees</code></p>
<pre>
+-------------+----------+
| Column Name | Type |
+-------------+----------+
| employee_id | int |
| name | varchar |
| manager_id | int |
| salary | int |
+-------------+----------+
In SQL, employee_id is the primary key for this table.
This table contains information about the employees, their salary, and the ID of their manager. Some employees do not have a manager (manager_id is null).
</pre>
<p>&nbsp;</p>
<p>Find the IDs of the employees whose salary is strictly less than <code>$30000</code> and whose manager left the company. When a manager leaves the company, their information is deleted from the <code>Employees</code> table, but the reports still have their <code>manager_id</code> set to the manager that left.</p>
<p>Return the result table ordered by <code>employee_id</code>.</p>
<p>The result format is in the following example.</p>
<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<pre>
<strong>Input: </strong>
Employees table:
+-------------+-----------+------------+--------+
| employee_id | name | manager_id | salary |
+-------------+-----------+------------+--------+
| 3 | Mila | 9 | 60301 |
| 12 | Antonella | null | 31000 |
| 13 | Emery | null | 67084 |
| 1 | Kalel | 11 | 21241 |
| 9 | Mikaela | null | 50937 |
| 11 | Joziah | 6 | 28485 |
+-------------+-----------+------------+--------+
<strong>Output:</strong>
+-------------+
| employee_id |
+-------------+
| 11 |
+-------------+
<strong>Explanation:</strong>
The employees with a salary less than $30000 are 1 (Kalel) and 11 (Joziah).
Kalel&#39;s manager is employee 11, who is still in the company (Joziah).
Joziah&#39;s manager is employee 6, who left the company because there is no row for employee 6 as it was deleted.
</pre>

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<p>Table: <code>Users</code></p>
<pre>
+---------------+---------+
| Column Name | Type |
+---------------+---------+
| user_id | int |
| name | varchar |
| mail | varchar |
+---------------+---------+
user_id is the primary key (column with unique values) for this table.
This table contains information of the users signed up in a website. Some e-mails are invalid.
</pre>
<p>&nbsp;</p>
<p>Write a solution to find the users who have <strong>valid emails</strong>.</p>
<p>A valid e-mail has a prefix name and a domain where:</p>
<ul>
<li><strong>The prefix name</strong> is a string that may contain letters (upper or lower case), digits, underscore <code>&#39;_&#39;</code>, period <code>&#39;.&#39;</code>, and/or dash <code>&#39;-&#39;</code>. The prefix name <strong>must</strong> start with a letter.</li>
<li><strong>The domain</strong> is <code>&#39;@leetcode.com&#39;</code>.</li>
</ul>
<p>Return the result table in <strong>any order</strong>.</p>
<p>The result format is in the following example.</p>
<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<pre>
<strong>Input:</strong>
Users table:
+---------+-----------+-------------------------+
| user_id | name | mail |
+---------+-----------+-------------------------+
| 1 | Winston | winston@leetcode.com |
| 2 | Jonathan | jonathanisgreat |
| 3 | Annabelle | bella-@leetcode.com |
| 4 | Sally | sally.come@leetcode.com |
| 5 | Marwan | quarz#2020@leetcode.com |
| 6 | David | david69@gmail.com |
| 7 | Shapiro | .shapo@leetcode.com |
+---------+-----------+-------------------------+
<strong>Output:</strong>
+---------+-----------+-------------------------+
| user_id | name | mail |
+---------+-----------+-------------------------+
| 1 | Winston | winston@leetcode.com |
| 3 | Annabelle | bella-@leetcode.com |
| 4 | Sally | sally.come@leetcode.com |
+---------+-----------+-------------------------+
<strong>Explanation:</strong>
The mail of user 2 does not have a domain.
The mail of user 5 has the # sign which is not allowed.
The mail of user 6 does not have the leetcode domain.
The mail of user 7 starts with a period.
</pre>