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https://github.com/alokshandilya/sql50-leetcode
SQL 50 leetcode | solutions | postgres
https://github.com/alokshandilya/sql50-leetcode
leetcode postgresql sql
Last synced: 3 days ago
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SQL 50 leetcode | solutions | postgres
- Host: GitHub
- URL: https://github.com/alokshandilya/sql50-leetcode
- Owner: alokshandilya
- Created: 2025-02-12T05:04:18.000Z (3 days ago)
- Default Branch: main
- Last Pushed: 2025-02-12T05:49:35.000Z (3 days ago)
- Last Synced: 2025-02-12T06:44:31.889Z (3 days ago)
- Topics: leetcode, postgresql, sql
- Homepage:
- Size: 2.93 KB
- Stars: 1
- Watchers: 1
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
Awesome Lists containing this project
README
# Top SQL 50 Study Plan (LeetCode)
This repository contains solutions to the **Top SQL 50 Study Plan** from [LeetCode](https://leetcode.com/studyplan/top-sql-50/) using **PostgreSQL**. Each problem is linked to its corresponding LeetCode page, and solutions are provided in PostgreSQL syntax.
## Select
#### 1. [Recyclable and Low Fat Products (1757)](https://leetcode.com/problems/recyclable-and-low-fat-products/)
```sql
SELECT
product_id
FROM
Products
WHERE
low_fats = 'Y'
AND
recyclable = 'Y';
```
#### 2. [Find Customer Referee (584)](https://leetcode.com/problems/find-customer-referee/)
```sql
SELECT
name
FROM
Customer
WHERE
referee_id <> 2
OR
referee_id IS NULL;
```
> **NOTE:** The `<>`, `!=` operator is used to compare two values and return `TRUE` if they are not equal, and `FALSE` otherwise.
```sql
SELECT
NULL <> 2
AS result;
-- output: NULL
```
#### 3. [Big Countries (595)](https://leetcode.com/problems/big-countries/)
```sql
SELECT
name,
population,
area
FROM
World
WHERE
area >= 3000000
OR
population >= 25000000;
```
#### 4. [Article Views I (1148)](https://leetcode.com/problems/article-views-i/)
```sql
SELECT
DISTINCT
author_id AS id
FROM
Views
WHERE
author_id = viewer_id
ORDER BY
id; -- or 1 (1st selected column) author_id/id)
```
#### 5. [Invalid Tweets (1683)](https://leetcode.com/problems/invalid-tweets/)
```sql
SELECT
tweet_id
FROM
Tweets
WHERE
LENGTH(content) > 15;
```
> [PostgreSQL string functions](https://www.postgresql.org/docs/current/functions-string.html) docs
> The `LENGTH()` function returns the length of a string in characters.
>
> ```
> length (text) → integer
> Returns the number of characters in the string.
> length('jose') → 4
> ```
## Basic Joins
> JOINs are used to combine rows from two or more tables based on a related column between them.
>
> - [Neon docs | PostgreSQL Joins](https://neon.tech/postgresql/postgresql-tutorial/postgresql-joins)
#### 6. [Replace Employee ID With The Unique Identifier (1378)](https://leetcode.com/problems/replace-employee-id-with-the-unique-identifier/)
```sql
SELECT
e.name,
u.unique_id
FROM
Employees e
LEFT JOIN
EmployeeUNI u
ON e.id = u.id;
```
#### 7. [Product Sales Analysis I (1068)](https://leetcode.com/problems/product-sales-analysis-i/)
```sql
SELECT
p.product_name,
s.year,
s.price
FROM
Sales s
NATURAL JOIN
Product p
```
#### 8. [Customer Who Visited but Did Not Make Any Transactions (1581)](https://leetcode.com/problems/customer-who-visited-but-did-not-make-any-transactions)
```sql
SELECT
v.customer_id,
COUNT(*)
AS count_no_trans
FROM
Visits v
LEFT JOIN
Transactions t
ON t.visit_id = v.visit_id
WHERE
t.transaction_id
IS NULL
GROUP BY
v.customer_id;
```
#### 9. [Rising Temperature (197)](https://leetcode.com/problems/rising-temperature/)
```sql
SELECT
w2.id
FROM
Weather w1
INNER JOIN
Weather w2
ON w2.temperature > w1.temperature
WHERE
w2.recordDate::date - w1.recordDate::date = 1
```
#### 10. [Average Time of Process per Machine (1661)](https://leetcode.com/problems/average-time-of-process-per-machine/)
```sql
SELECT
a2.machine_id,
ROUND(AVG(a2.timestamp - a1.timestamp)::numeric, 3) -- or, decimal
AS processing_time
FROM
Activity a1
INNER JOIN
Activity a2
ON a2.machine_id = a1.machine_id
WHERE
a2.activity_type = 'end'
AND a1.activity_type = 'start'
GROUP BY
a2.machine_id
```
> The `::` operator is used to cast a value to a specific data type.
>
> - [PostgreSQL numeric data types](https://www.postgresql.org/docs/current/datatype-numeric.html) docs
#### 11. [Employee Bonus (577)](https://leetcode.com/problems/employee-bonus/)
```sql
SELECT
e.name,
b.bonus
FROM
Employee e
LEFT JOIN
Bonus b
ON b.empId = e.empId
WHERE
b.bonus < 1000
OR
b.bonus IS NULL;
```
#### 12. [Students and Examinations (1280)](https://leetcode.com/problems/students-and-examinations/)
```sql
SELECT
st.student_id,
st.student_name,
su.subject_name,
COUNT(e.subject_name)
AS attended_exams
FROM
Students st
CROSS JOIN
Subjects su
LEFT JOIN
Examinations e
ON
e.student_id = st.student_id
AND
e.subject_name = su.subject_name
GROUP BY
st.student_id,
st.student_name,
su.subject_name
ORDER BY
st.student_id,
su.subject_name;
```
#### 13. [Managers with at Least 5 Direct Reports (570)](https://leetcode.com/problems/managers-with-at-least-5-direct-reports)
```sql
-- using subquery
SELECT
name
FROM
Employee
WHERE
id IN (
SELECT
managerId
FROM
Employee
WHERE
managerId
IS NOT NULL
GROUP BY
managerId
HAVING
COUNT(*) >= 5
)
-- using join
SELECT
e1.name
FROM
Employee e1
JOIN
Employee e2
ON
e2.managerId = e1.id
WHERE
e2.managerId
IS NOT NULL
GROUP BY
e1.name, e1.id -- allow multiple name
HAVING
COUNT(*) >= 5;
```
#### 14. [Confirmation Rate (1934)](https://leetcode.com/problems/confirmation-rate/)
```sql
SELECT
s.user_id,
ROUND(
COUNT(*) FILTER (WHERE c.action='confirmed')::decimal / COUNT(*),
2
) AS confirmation_rate
FROM
Signups s
LEFT JOIN
Confirmations c
ON
c.user_id = s.user_id
GROUP BY
s.user_id
```
## Basic Aggregate Functions
#### 15. [Not Boring Movies (620)](https://leetcode.com/problems/not-boring-movies)
```sql
SELECT
*
FROM
Cinema
WHERE
id % 2 = 1
AND
description <> 'boring'
ORDER BY
rating DESC;
```
#### 16. [Average Selling Price (1251)](https://leetcode.com/problems/average-selling-price)
```sql
SELECT
p.product_id,
COALESCE(
ROUND(
SUM(u.units * p.price)::decimal / SUM(u.units), 2
), 0
) AS average_price
FROM
Prices p
LEFT JOIN
UnitsSold u
ON u.product_id = p.product_id
AND
u.purchase_date BETWEEN p.start_date AND p.end_date
GROUP BY
p.product_id
```
## Contributing
If you'd like to contribute, feel free to fork this repository and submit a pull request with your solutions or improvements. Make sure to follow the same format for consistency.