/* Selected fields from the 'user' and 'oauth_app' tables */
/* Create a 'key' from the 'userId' and 'app.name' for grouping purposes */
SELECT
u.username, app.name AS appname, concat(token."userId", app.name) as key

FROM public.oauth_token token

/* Join to the 'user' table */
INNER JOIN public.user u
    ON token."userId" = u.id

/* Join to the 'oauth_app' table */
INNER JOIN public.oauth_app app
    ON app.id = token."appId"