pub_db=# SELECT COALESCE(j.site_id, m.site_id) AS site_id, vars, tags FROM scrape_jsvariablestotrack j FULL OUTER JOIN scrape_metatagstotrack m ON j.site_id = m.site_id;
 site_id |                vars                |            tags
---------+------------------------------------+-----------------------------
      76 |                                    | test,of,tags,but,no,js,vars
      77 | test,of,js,vars,but,no,meta,tags   |
    4255 | dialog                             |
    4335 | webServer,b2cDomain,_ln,IpLanguage | googlebot,Keywords
    4357 | _hbq,_ar,_rf,_f                    | robots,Description,Keywords
(5 rows)