在concat查询中应用distinct

Question

我为三个表编写了一个连接查询，连接这三个表的列。但是在最后一个表keywords列中只有一个值，但在重复汇总时会重复该值。

SELECT
  g.goal_id,
  concat(coalesce(rk.keyword, ''),
         coalesce(gr.description, ''),
         coalesce(cd.keywords, ''))
FROM goal g
  LEFT OUTER JOIN resource_keyword rk ON (g.creater_id = rk.refference_id AND
                                          g.creater_id = :userId)
  LEFT OUTER JOIN groups gr ON gr.creater_id = g.creater_id
  LEFT OUTER JOIN communication_detail cd ON cd.party_id = gr.creater_id
LIMIT 5

实际结果：

      goal_id      concat

      296          noseDaily walk,sad,err
      296          Healthy is a goalDaily walk,sad,err
      296          Healthylife a healthy dayDaily walk,sad,err
      296          tasty foodDaily walk,sad,err
      296          healthygradeDaily walk,sad,err

预期结果：

      goal_id       concat

      296          noseDaily walk,sad,err
      296          Healthy is a goalDaily walk
      296          Healthylife a healthy dayDaily walk
      296          tasty foodDaily walk
      296          healthygradeDaily walk

这里很遗憾，错误属于第三个表，只有一个值用逗号分隔，但它会被附加到每一行。