How to remove duplicates, which are generated with

问题:

Does anyone an idea how to rewrite following SQL query to generate results, that would contains only one occurrence of name? (results grouped by user).

The query

SELECT array_to_string(array_agg(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

Executable query is avaiable on sqlfiddle.com. Click on Run SQL button and you will result, which contains Frantisek Smith twice

回答1:

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