awesee · awesee · Feb 4, 2020 · Feb 4, 2020
diff --git a/problems/ads-performance/README.md b/problems/ads-performance/README.md
@@ -11,4 +11,60 @@
 
 ## [1322. Ads Performance (Easy)](https://leetcode.com/problems/ads-performance "")
 
+<p>Table: <code>Ads</code></p>
+<pre>
++---------------+---------+
+| Column Name   | Type    |
++---------------+---------+
+| ad_id         | int     |
+| user_id       | int     |
+| action        | enum    |
++---------------+---------+
+(ad_id, user_id) is the primary key for this table.
+Each row of this table contains the ID of an Ad, the ID of a user and the action taken by this user regarding this Ad.
+The action column is an ENUM type of ('Clicked', 'Viewed', 'Ignored').
+</pre>
+
+A company is running Ads and wants to calculate the performance of each Ad.
 
+Performance of the Ad is measured using Click-Through Rate (CTR) where:
+
+[[image-blog:Leetcode: Ads Performance][https://raw.githubusercontent.com/dennyzhang/code.dennyzhang.com/master/problems/ads-performance/ctrformula.png]]
+
+Write an SQL query to find the ctr of each Ad.
+
+Round ctr to 2 decimal points. Order the result table by ctr in descending order and by ad_id in ascending order in case of a tie.
+
+The query result format is in the following example:
+<pre>
+Ads table:
++-------+---------+---------+
+| ad_id | user_id | action  |
++-------+---------+---------+
+| 1     | 1       | Clicked |
+| 2     | 2       | Clicked |
+| 3     | 3       | Viewed  |
+| 5     | 5       | Ignored |
+| 1     | 7       | Ignored |
+| 2     | 7       | Viewed  |
+| 3     | 5       | Clicked |
+| 1     | 4       | Viewed  |
+| 2     | 11      | Viewed  |
+| 1     | 2       | Clicked |
++-------+---------+---------+
+Result table:
++-------+-------+
+| ad_id | ctr   |
++-------+-------+
+| 1     | 66.67 |
+| 3     | 50.00 |
+| 2     | 33.33 |
+| 5     | 0.00  |
++-------+-------+
+for ad_id = 1, ctr = (2/(2+1)) * 100 = 66.67
+for ad_id = 2, ctr = (1/(1+2)) * 100 = 33.33
+for ad_id = 3, ctr = (1/(1+1)) * 100 = 50.00
+for ad_id = 5, ctr = 0.00, Note that ad_id has no clicks or views.
+Note that we don't care about Ignored Ads.
+Result table is ordered by the ctr. in case of a tie we order them by ad_id
+</pre>
diff --git a/problems/list-the-products-ordered-in-a-period/README.md b/problems/list-the-products-ordered-in-a-period/README.md
@@ -11,4 +11,80 @@
 
 ## [1327. List the Products Ordered in a Period (Easy)](https://leetcode.com/problems/list-the-products-ordered-in-a-period "")
 
+SQL Schema
+<p>Table: <code>Products</code></p>
+<pre>
++------------------+---------+
+| Column Name      | Type    |
++------------------+---------+
+| product_id       | int     |
+| product_name     | varchar |
+| product_category | varchar |
++------------------+---------+
+product_id is the primary key for this table.
+This table contains data about the company's products.
+</pre>
 
+<p>Table: <code>Orders</code></p>
+<pre>
++---------------+---------+
+| Column Name   | Type    |
++---------------+---------+
+| product_id    | int     |
+| order_date    | date    |
+| unit          | int     |
++---------------+---------+
+There is no primary key for this table. It may have duplicate rows.
+product_id is a foreign key to Products table.
+unit is the number of products ordered in order_date.
+</pre>
+
+Write an SQL query to get the names of products with greater than or equal to 100 units ordered in February 2020 and their amount.
+
+Return result table in any order.
+
+The query result format is in the following example:
+<pre>
+Products table:
++-------------+-----------------------+------------------+
+| product_id  | product_name          | product_category |
++-------------+-----------------------+------------------+
+| 1           | Leetcode Solutions    | Book             |
+| 2           | Jewels of Stringology | Book             |
+| 3           | HP                    | Laptop           |
+| 4           | Lenovo                | Laptop           |
+| 5           | Leetcode Kit          | T-shirt          |
++-------------+-----------------------+------------------+
+
+Orders table:
++--------------+--------------+----------+
+| product_id   | order_date   | unit     |
++--------------+--------------+----------+
+| 1            | 2020-02-05   | 60       |
+| 1            | 2020-02-10   | 70       |
+| 2            | 2020-01-18   | 30       |
+| 2            | 2020-02-11   | 80       |
+| 3            | 2020-02-17   | 2        |
+| 3            | 2020-02-24   | 3        |
+| 4            | 2020-03-01   | 20       |
+| 4            | 2020-03-04   | 30       |
+| 4            | 2020-03-04   | 60       |
+| 5            | 2020-02-25   | 50       |
+| 5            | 2020-02-27   | 50       |
+| 5            | 2020-03-01   | 50       |
++--------------+--------------+----------+
+
+Result table:
++--------------------+---------+
+| product_name       | unit    |
++--------------------+---------+
+| Leetcode Solutions | 130     |
+| Leetcode Kit       | 100     |
++--------------------+---------+
+
+Products with product_id = 1 is ordered in February a total of (60 + 70) = 130.
+Products with product_id = 2 is ordered in February a total of 80.
+Products with product_id = 3 is ordered in February a total of (2 + 3) = 5.
+Products with product_id = 4 was not ordered in February 2020.
+Products with product_id = 5 is ordered in February a total of (50 + 50) = 100.
+</pre>
diff --git a/problems/number-of-transactions-per-visit/README.md b/problems/number-of-transactions-per-visit/README.md
@@ -11,4 +11,84 @@
 
 ## [1336. Number of Transactions per Visit (Medium)](https://leetcode.com/problems/number-of-transactions-per-visit "")
 
+<p>Table: <code>Visits</code></p>
+<pre>
++---------------+---------+
+| Column Name   | Type    |
++---------------+---------+
+| user_id       | int     |
+| visit_date    | date    |
++---------------+---------+
+(user_id, visit_date) is the primary key for this table.
+Each row of this table indicates that user_id has visited the bank in visit_date.
+</pre>
 
+<p>Table: <code>Transactions</code></p>
+<pre>
++------------------+---------+
+| Column Name      | Type    |
++------------------+---------+
+| user_id          | int     |
+| transaction_date | date    |
+| amount           | int     |
++------------------+---------+
+There is no primary key for this table, it may contain duplicates.
+Each row of this table indicates that user_id has done a transaction of amount in transaction_date.
+It is guaranteed that the user has visited the bank in the transaction_date.(i.e The Visits table contains (user_id, transaction_date) in one row)
+</pre>
+
+Write an SQL query to find how many users visited the bank and didn't do any transactions, how many visited the bank and did one transaction and so on.
+
+The result table will contain two columns transactions_count which is the number of transactions done in one visit and visits_count which is the corresponding number of users who did transactions_count in one visit to the bank. transactions_count should take all values from 0 to max(transactions_count) done by one or more users.
+
+Order the result table by transactions_count.
+
+The query result format is in the following example:
+
+<pre>
+Visits table:
++---------+------------+
+| user_id | visit_date |
++---------+------------+
+| 1       | 2020-01-01 |
+| 2       | 2020-01-02 |
+| 12      | 2020-01-01 |
+| 19      | 2020-01-03 |
+| 1       | 2020-01-02 |
+| 2       | 2020-01-03 |
+| 1       | 2020-01-04 |
+| 7       | 2020-01-11 |
+| 9       | 2020-01-25 |
+| 8       | 2020-01-28 |
++---------+------------+
+Transactions table:
++---------+------------------+--------+
+| user_id | transaction_date | amount |
++---------+------------------+--------+
+| 1       | 2020-01-02       | 120    |
+| 2       | 2020-01-03       | 22     |
+| 7       | 2020-01-11       | 232    |
+| 1       | 2020-01-04       | 7      |
+| 9       | 2020-01-25       | 33     |
+| 9       | 2020-01-25       | 66     |
+| 8       | 2020-01-28       | 1      |
+| 9       | 2020-01-25       | 99     |
++---------+------------------+--------+
+Result table:
++--------------------+--------------+
+| transactions_count | visits_count |
++--------------------+--------------+
+| 0                  | 4            |
+| 1                  | 5            |
+| 2                  | 0            |
+| 3                  | 1            |
++--------------------+--------------+
+Users 1, 2, 12 and 19 visited the bank in 2020-01-01, 2020-01-02, 2020-01-01 and 2020-01-03 respectively, and didn't do any transactions.
+So we have visits_count = 4 for transactions_count = 0.
+Users 2, 7 and 8 visited the bank in 2020-01-03, 2020-01-11 and 2020-01-28 respectively, and did one transaction.
+User 1 Also visited the bank in 2020-01-02 and 2020-01-04 and did one transaction each day.
+So we have total visits_count = 5 for transactions_count = 1.
+For transactions_count = 2 we don't have any users who visited the bank and did two transactions.
+For transactions_count = 3 we have user 9 who visited the bank in 2020-01-25 and did three transactions.
+Note that we stopped at transactions_count = 3 as this is the maximum number of transactions done by one user in one visit to the bank.
+</pre>