text: SELECT c.oid, conname as name, relname, nspname, description as comment ,
         pg_get_expr(conbin, conrelid, true) as consrc
      FROM pg_constraint c
      JOIN pg_class cl ON cl.oid=conrelid
      JOIN pg_namespace nl ON nl.oid=relnamespace
  LEFT OUTER JOIN
      pg_description des ON (des.objoid=c.oid AND
                             des.classoid='pg_constraint'::regclass)
  WHERE contype = 'c'
      AND conrelid = {{ tid }}::oid
  {% if cid %}
      AND c.oid = {{ cid }}::oid
  {% endif %}