Hackerrank - SQL - Weather Observation Station 7

#sql #beginners #hackerrank #learning

https://github.com/mrpunkdasilva/hackerrank/tree/main/sql/basic/weather-observartion-station-7

Problem Description

Query the list of CITY names ending with vowels (a, e, i, o, u) from STATION. Your result cannot contain duplicates.

Input Format

The STATION table is described as follows:

Field	Type
ID	NUMBER
CITY	VARCHAR2(21)
STATE	VARCHAR2(2)
LAT_N	NUMBER
LONG_W	NUMBER

where LAT_N is the northern latitude and LONG_W is the western longitude.

Solution Approach

Use a SELECT statement with the DISTINCT keyword to retrieve unique CITY names
Apply a WHERE clause with conditions:
- Ensure LAT_N and LONG_W are not NULL
- Check if the last character of the CITY name is a vowel using the SUBSTRING function and the IN operator

Step-by-Step Explanation

Start with the SELECT statement using DISTINCT to get unique city names:

   SELECT DISTINCT CITY

Specify the table to query from:

   FROM STATION

Add the WHERE clause with conditions:
- Check for valid latitude and longitude values
- Use SUBSTRING with a negative index to extract the last character of each CITY name
- Convert it to lowercase with LOWER
- Check if it's a vowel using the IN operator

   WHERE 
       (LAT_N IS NOT NULL) AND
       (LONG_W IS NOT NULL) AND 
       LOWER(SUBSTRING(CITY, -1)) IN ('a', 'e', 'i', 'o', 'u')

The final query:

   SELECT 
       DISTINCT CITY
   FROM
       STATION
   WHERE 
       (LAT_N IS NOT NULL) AND
       (LONG_W IS NOT NULL) AND 
       LOWER(SUBSTRING(CITY, -1)) IN ('a', 'e', 'i', 'o', 'u')
   ;