问题
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
Result:
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)>
回答1:
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
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
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
.
来源:https://stackoverflow.com/questions/54494557/using-fragment-group-by-together-with-postgres-ecto