Query the list of CITY names from STATION which have vowels (i.e., a, e, i, o, and u) as both their first and last characters. Your result cannot contain duplicates.

This question seems to be related to SQL (Structured Query Language), which is used to manage and manipulate databases. Here is a step-by-step guide on how to solve it:

1. First, you need to select the CITY column from the STATION table. This can be done with the following SQL command: SELECT CITY FROM STATION.

2. Next, you need to filter the cities that have vowels as their first and last characters. You can use the LIKE keyword in SQL to do this. The LIKE keyword allows you to use wildcards in your conditions. The % wildcard allows for any number of characters, and _ allows for a single character.

3. To specify that the first character should be a vowel, you can use a condition like this: CITY LIKE '[aeiou]%. This means that the CITY should start with any of the characters inside the brackets.

4. To specify that the last character should also be a vowel, you can use a condition like this: CITY LIKE '%[aeiou]'. This means that the CITY should end with any of the characters inside the brackets.

5. Combining these conditions, your SQL command should look like this: SELECT CITY FROM STATION WHERE CITY LIKE '[aeiou]%' AND CITY LIKE '%[aeiou]'.

6. Finally, to ensure that your result does not contain duplicates, you can use the DISTINCT keyword. This keyword will eliminate any duplicate rows in your result. Your final SQL command should look like this: SELECT DISTINCT CITY FROM STATION WHERE CITY LIKE '[aeiou]%' AND CITY LIKE '%[aeiou]'.

Please note that SQL syntax can vary slightly between different database systems, so you might need to adjust the command depending on the specific system you are using. For example, some systems might require you to use REGEXP instead of LIKE for pattern matching.