Create an array from the two columns, the aggregate the array: select id, array_agg(array[x,y]) from the_table group by id; Note that the default text representation of arrays uses curly braces ( {..}) not square brackets ([..])
You can use the distinct keyword inside array_agg: SELECT ARRAY_TO_STRING(ARRAY_AGG(DISTINCT CONCAT(u.firstname, ‘ ‘, u.lastname)), ‘, ‘) FROM log_has_item logitem INNER JOIN log log ON log.id = logitem.log_id INNER JOIN worker u ON log.worker_id = u.id WHERE logitem.company_id = 1 SQLFiddle with this example
Use an ORDER BY, like this example from the manual: SELECT array_agg(a ORDER BY b DESC) FROM table;