In which ways can you compare fields FIRST_NAME and LAST_NAME in a SELECT statement?

The correct choice demonstrates a proper method for comparing the fields FIRST_NAME and LAST_NAME in a SELECT statement by using an alias for the table being queried.

When employing the SELECT statement with an alias, the syntax makes it clear which fields are being referenced, and it enhances readability, especially in queries involving multiple tables or extensive fields. In this case, the alias "a" is clearly defined for the "users" table, allowing for succinct comparison of a.first_name to a.last_name.

In this context, employing an alias provides clarity within the SQL statement. It clearly indicates that both columns are being pulled from the same "users" table, avoiding potential confusion with fields of the same name across different tables in more complex queries. Therefore, it is critical to maintain the integrity of the comparison while ensuring that the syntax adheres to SQL standards.

The other choices either do not correctly implement an alias or make assumptions that can lead to ambiguity or errors. Utilizing an alias, as shown in the correct answer, is a best practice in SQL for ensuring that the comparisons are explicit and that the code is maintainable and understandable.