Python peewee：如何在连接前选择一列上的不同值？

Question

I try to join a second table (PageLikes) on a first Table (PageVisits) after selecting only distinct values on one column of the first table with the python ORM peewee.

In pure SQL I can do this:

SELECT DISTINCT(pagevisits.visitor_id), pagelikes.liked_item FROM pagevisits
INNER JOIN pagelikes on pagevisits.visitor_id = pagelikes.user_id

In peewee with python I have tried:

query = (Page.select(
         fn.Distinct(Pagevisits.visitor_id),
         PageLikes.liked_item)
         .join(PageLIkes)

This gives me an error: distinct() takes 1 positional argument but 2 were given

The only way I can and have used distinct with peewee is like this:

query = (Page.select(
         Pagevisits.visitor_id,
         PageLikes.liked_item)
         .distinct()

which does not seem to work for my scenario.

So how can I select only distinct values in one table based on one column before I join another table with peewee?

Answer 1

I don't believe you should be encountering an error using fn.DISTINCT() in that way. I'm curious to see the full traceback. In my testing locally, I have no problems running something like:

query = (PageVisits
         .select(fn.DISTINCT(PageVisits.visitor_id), PageLikes.liked_item)
         .join(PageLikes))

Which produces SQL equivalent to what you're after. I'm using the latest peewee code btw.

Answer 2

As Papooch suggested, calling distinct on the Model seems to work:

distinct_visitors = (Pagevisits
                            .select(
                                Pagevisits.visitor_id.distinct().alias("visitor")
                            )
                            .where(Pagevisits.page_id == "Some specifc page")
                            .alias('distinct_visitors')
                            )


query = (Pagelikes
         .select(fn.Count(Pagelikes.liked_item),
         )
         .join(distinct_visitors, on=(distinct_visitors.c.visitor = Pagelikes.user_id))
         .group_by(Pagelikes.liked_item)
         )