Find unused indexes in postgres

SELECT s.schemaname,
       s.relname AS tablename,
       s.indexrelname AS indexname,
       pg_relation_size(s.indexrelid) AS index_size,
       s.idx_scan
FROM pg_catalog.pg_stat_user_indexes s
         JOIN pg_catalog.pg_index i ON s.indexrelid = i.indexrelid
WHERE s.idx_scan > 0      -- has never been scanned
  AND 0 <>ALL (i.indkey)  -- no index column is an expression
  AND NOT i.indisunique   -- is not a UNIQUE index
  AND NOT EXISTS          -- does not enforce a constraint
    (SELECT 1 FROM pg_catalog.pg_constraint c
     WHERE c.conindid = s.indexrelid)
ORDER BY pg_relation_size(s.indexrelid) DESC;