gistfile1.sql

SELECT 
    sender.jid || COALESCE('/' || sender_resource, '') AS sender,
    recipient.jid || COALESCE('/' || recipient_resource, '') AS recipient,
    message.id, message.type, message.body, message.thread
FROM messages message
JOIN identificators sender
    ON sender.id = message.sender
JOIN identificators recipient
    ON recipient.id = message.recipient