Gathering Document Statistics

ts_stat(sqlquery text, [ weights text, ]
        OUT word text, OUT ndoc integer,
        OUT nentry integer) returns setof record

postgres=# SELECT * FROM ts_stat('SELECT to_tsvector(''english'', sr_reason_sk) FROM tpcds.store_returns WHERE sr_customer_sk < 10') ORDER BY nentry DESC, ndoc DESC, word LIMIT 10;
   word | ndoc | nentry
------+------+--------
 32   |    2 |      2
 33   |    2 |      2
 1    |    1 |      1
 10   |    1 |      1
 13   |    1 |      1
 14   |    1 |      1
 15   |    1 |      1
 17   |    1 |      1
 20   |    1 |      1
 22   |    1 |      1
(10 rows)

postgres=# SELECT * FROM ts_stat('SELECT to_tsvector(''english'', sr_reason_sk) FROM tpcds.store_returns WHERE sr_customer_sk < 10', 'a') ORDER BY nentry DESC, ndoc DESC, word LIMIT 10;
 word | ndoc | nentry
------+------+--------
(0 rows)