如何删除使用array_agg postgres函数生​​成的重复项

Question

有没有人知道如何重写以下SQL查询来生成结果,那将只包含一次出现的名称？(按用户分组的结果).

查询

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

可执行查询可在sqlfiddle.com上获得.单击Run SQL按钮,结果将包含两次Frantisek Smith

Answer 1

您可以在distinct里面使用关键字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有这个例子

Answer 2

ARRAY_TO_STRING(ARRAY_AGG(当一个简单的STRING_AGG操作如下时，无需在房子周围走来走去（代码可在此处的小提琴上找到）：

--
-- Simplified
--

SELECT
  DISTINCT
  STRING_AGG
  (
    DISTINCT CONCAT(w.firstname, ' ', w.lastname), ', '
  ) AS "The workers"
FROM log_item li
INNER JOIN log l ON li.log_id = l.id 
INNER JOIN worker w ON l.worker_id = w.id
WHERE li.company_id = 1;

结果：

                The workers
Frantisek Smith, Peter Duff