hackerrank(sql): Weather obs station 5

description: Notes and solutions on the HackerRank SQL challenges for MySQL/MariaDB.

---

# Baisc HackerRank SQL Challenges

# Basic HackerRank SQL Challenges

## Intro

Unless otherwise noted, assume these examples where tested on MySQL and MySQL CLI. I prefer MariaDB and PostgreSQL by it seems HackerRank does not provide any of those (as of June 18, 2023 at least).

Unless otherwise noted, assume these examples where tested on MySQL and MySQL CLI.

I prefer MariaDB and PostgreSQL by it seems HackerRank does not provide any of those (as of June 18, 2023 at least).

Also, we'll try to stick to standard-compliant (and shy away from vendor-specific features and syntax) SQL whenever possible for max portability.

```{note}

RackerRank SQL challenges come in three main levels of difficulty:

- Advanced

This page deals with the basic ones.

```

![HackerRank SQL MySQL / MariaDB Dropdown Option](/staticassets/hackerrank-sql-mysql-db-dropdown.png)

  LOWER(SUBSTR(title, 1, 1))

  IN('a', 'e', 'i', 'o', 'u');

```

## Weather Observation Station 5

- [Weather Observation Station 5 :: HackerRank Easy SQL Challenge](https://www.hackerrank.com/challenges/weather-observation-station-5)

### UNION ALL of two queries

One approach is to use two queries: one for the city name length, and another one for the min city name length, limit by 1, and union the results to create a single resulting tabular structure:

```sql

(SELECT

    city

  ,  LENGTH(city) AS len_city

FROM station

ORDER BY len_city ASC, city DESC

LIMIT 1)

UNION ALL

(SELECT

    city

  , LENGTH(city) AS len_city

FROM station

ORDER BY len_city DESC, city DESC

LIMIT 1);

```

### WHERE IN union of subquery

Or creating a sub-table to select the lengths from.

First, select the max and min lengths:

```sql

SELECT MAX(LENGTH(city)) FROM station

UNION ALL

SELECT MIN(LENGTH(city)) FROM station;

```

It returns a tabular structures with the max and min lengths, which can be used in a `WHEER/IN` clause:

```sql

SELECT

    city

  , LENGTH(city)

FROM station

WHERE LENGTH(city) IN (

  SELECT MAX(LENGTH(city)) FROM station

  UNION ALL

  SELECT MIN(LENGTH(city)) FROM station

)

ORDER BY LENGTH(city) DESC, city;

```