Hackerrank - SQL - Weather Observation Station 6

https://github.com/mrpunkdasilva/hackerrank/tree/main/sql/basic/weather-observartion-station-6

Problem Description

Query the list of CITY names starting with vowels (i.e., a, e, i, o, or 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

1. Use a SELECT statement to retrieve the CITY column from the STATION table
2. Apply a WHERE clause with conditions:
   • Ensure LAT_N and LONG_W are not NULL
   • Check if the first character of the CITY name is a vowel using the SUBSTRING function and the IN operator

Step-by-Step Explanation

1. Start with the SELECT statement to retrieve the CITY column:

   SELECT CITY

1. Specify the table to query from:

   FROM STATION

1. Add the WHERE clause with conditions:
   • Check for valid latitude and longitude values
   • Use SUBSTRING to extract the first 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,1,1)) IN ('a', 'e', 'i', 'o', 'u')

1. The final query:

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

Expected Output

The query will return a list of city names from the STATION table where the first character is a vowel (a, e, i, o, or u). The result will not contain duplicate city names.