Postresql child record ids as an array

children_ids.sql

-- I don't understand how totally this works but it does so

CREATE AGGREGATE children_ids (anyelement)
(                          
    sfunc = array_append,
    stype = anyarray,
    initcond = '{}'
);

-- then you can do

SELECT                                  
  DISTINCT visitor.id, 
  name, 
  children_ids(visitor_id) as kids
FROM 
  visitor
  LEFT JOIN visits ON visitor.id = visits.visitor_id 
GROUP BY
  visitor.id

-- and, in yii the $kids fields with be a string like so
-- "{1421,4334,333,123214}"