Filtering out duplicate domains from URL column using Postgres full-text search parsers

I have a PostgreSQL database containing pages and links downloaded by a web crawler, with the following tables: pages ---------- id: Integer (primary key) url: String (unique) title: String text: String html: String last_visit: DateTime word_pos: TSVECTOR links ---------- id Integer (primary key) source: String target: String link_text: String UNIQUE(source,target) crawls --------- id: Integer (primary key) query: String crawl_results ------------- id: Integer (primary key) score: Integer (constraint 0<=score<=1) crawl_id: Integer (foreign key, crawls.id) page_id: Integer (foreign key, pages.id) The source and target fields in the links table contain URLs. I am running the following query to extract scored links from the top-ranking search results, for pages that haven't been fetched yet: WITH top_results AS (SELECT page_id, score FROM crawl_results WHERE crawl_id=$1 ORDER BY score LIMIT 100) SELECT top_results.score, l.target FROM top_results JOIN pages p ON top_results.page_id=p.id JOIN links l on p.url=l.source WHERE NOT EXISTS (SELECT pp.id FROM pages pp WHERE l.target=pp.url) However, ***I would like to filter these results so that only one row is returned for a given domain (the one with the lowest score)***. So for instance, if I get (0.3, 'http://www.foo.com/bar ') and (0.8, 'http://www.foo.com/zor '), I only want the first because it has same domain foo.com and has the lower score. I was able to find documentation for the builtin full text search parsers, which can parse URLS and extract the hostname. For instance, I can extract the hostname from a URL as follows: SELECT token FROM ts_parse('default', 'http://www.foo.com ') WHERE tokid = 6; token ------------- www.foo.com (1 row) However, I can't figure out how I would integrate this into the above query to filter out duplicate domains from the results. And because this is the docs for "testing and debugging text search", I don't know if this use of ts_parse() is even related to how the URL parser is intended to be used in practice. ***How would I use the host parser in my query above to return one row per domain? Also, how would I appropriately index the links table for host and url lookup?***