使用片段&group_by和postgres&ecto?

问题描述

我正在努力使它与Postgres和Ecto一起使用.下面的查询在没有group_by的情况下可以正常工作，但我需要对似乎看不到的fragment字段进行分组.知道有什么问题吗?

I'm struggling to get this to work with Postgres and Ecto. The query below works fine without the group_by, but I need to group on the fragment field, which it can't seem to see. Any idea what's wrong with it?

  def query_clicks do
    from(Click)
    |> select(
      [c],
      [
        fragment("date_trunc('hour',?) as hour", c.inserted_at), c.link_id]
      )
    |> group_by([c], c.hour)
    |> Repo.all
  end

结果:

iex(1)> recompile; Shortr.LinkContext.query_clicks
[debug] QUERY ERROR source="clicks" db=1.2ms queue=4.9ms
SELECT date_trunc('hour',c0."inserted_at") as hour, c0."link_id" FROM "clicks" AS c0 GROUP BY c0."hour" []
** (Postgrex.Error) ERROR 42703 (undefined_column) column c0.hour does not exist

    query: SELECT date_trunc('hour',c0."inserted_at") as hour, c0."link_id" FROM "clicks" AS c0 GROUP BY c0."hour"
    (ecto_sql) lib/ecto/adapters/sql.ex:604: Ecto.Adapters.SQL.raise_sql_call_error/1
    (ecto_sql) lib/ecto/adapters/sql.ex:537: Ecto.Adapters.SQL.execute/5
    (ecto) lib/ecto/repo/queryable.ex:147: Ecto.Repo.Queryable.execute/4
    (ecto) lib/ecto/repo/queryable.ex:18: Ecto.Repo.Queryable.all/3
iex(1)>

推荐答案

在生成的SQL中，您调用 c0.hour ，而将列别名为 hour .应该是

In the resulting SQL you call c0.hour whereas you alias the column to hour. It should be

SELECT date_trunc('hour',c0."inserted_at") as hour, c0."link_id" FROM "clicks" AS c0 GROUP BY hour

在Ecto中，这将变成

In Ecto this would become

def query_clicks do
  from(Click)
  |> select(
    [c],
    [
      fragment("date_trunc('hour',?) as hour", c.inserted_at), c.link_id
    ]
  )
  |> group_by([c], fragment("hour"))
  |> Repo.all
end

另一个问题是 link_id ，SELECT子句中的任何字段都必须出现在GROUP BY子句中或为聚集体.例如，您还可以按 link_id 分组.

Another issue is the link_id, any field in the SELECT clause must appear in the GROUP BY clause or be an aggregrate. You could for example also group by link_id.

这篇关于使用片段&group_by和postgres&ecto?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！