Could you provide a SQL query to find the set of unique communicators from a table named messages containing the fields id, sender_id, receiver_id, and message?

Question Analysis

The question requires you to write a SQL query to identify a unique set of individuals or entities that have either sent or received a message. The table named messages contains several fields: id, sender_id, receiver_id, and message. The task is to determine all unique sender_id and receiver_id combined, which represents the set of unique communicators.

Answer

To find the set of unique communicators, you need to consider both sender_id and receiver_id fields from the messages table. You can utilize the SQL UNION operator to combine the results from these two fields, ensuring duplicates are removed to get unique entries.

SELECT sender_id AS communicator_id FROM messages
UNION
SELECT receiver_id AS communicator_id FROM messages;

Explanation:

• SELECT sender_id AS communicator_id: This part of the query selects all distinct sender_ids.
• UNION: Combines the results of both queries and removes any duplicates, ensuring each communicator is listed only once.
• SELECT receiver_id AS communicator_id: This part of the query selects all distinct receiver_ids.
• The result set, communicator_id, will contain a list of all unique communicators from both sender_id and receiver_id fields.