select count(*) -- rp.tag
from submission
inner join post rp on submission.id = rp.submission_id
where user_name = ?1
and lower(rp.tag) like ('%verified%')
and not lower(rp.tag) like ('%unverified%');

select count(*) rp.tag
from submission
inner join post rp on submission.id = rp.submission_id
where user_name = ?1
and lower(tag) like ('%verified%') and not lower(tag) like ('%unverified%')
LIMIT 1

CREATE INDEX subm_userName_tag_idx ON submission (user_name, lower(tag));

and lower(tag) like ('%verified%') and not lower(tag) like ('%unverified%')

SELECT count(*) FROM (
   SELECT             -- empty SELECT list
   FROM   submission
   JOIN   ...
   WHERE  ...
   LIMIT 1
   ) sub

SELECT EXISTS (
   SELECT FROM submission s
   JOIN   post p ON s.id = rp.submission_id
   WHERE  s.user_name = ?
   AND    p.tag ~* 'verified'
   AND    NOT p.tag ~* 'unverified'
   );

CREATE INDEX post_tag_gin_trgm_idx ON post USING gin (tag gin_trgm_ops);

UPDATE foo
SET    bar = 'baz'
WHERE  EXISTS ( ...) -- like above
AND    bar IS DISTINCT FROM 'baz' -- avoid empty updates