sqlite equivalent of row_number() over ( partition by …?

Question

I\'d like to know if it\'s possible to do the following using a single sqlite statement:

My table looks something like this:

|AnId|UserId|SomeDate|So         


        

Answer 1

As of Sqlite 3.25 window functions are supported. See https://www.sqlite.org/windowfunctions.html for details.

Answer 2

I needed to fetch the second row for each "object" in a table with a 1 to many relationship to the "object" table.

Usually in SQL this will be done using ROW_NUMBER() OVER(PARTITION BY object_id ORDER BY primary_id DESC)

In Sqlite I had to come up with this voodoo sub-query to get the same result

SELECT object_id, MAX(_id)
FROM (SELECT object_id, _id
FROM aTable
EXCEPT
SELECT object_id, MAX(_id)
FROM aTable
GROUP BY object_id)
GROUP BY object_id;

Note: The _id is the primary key of aTable and the object table has a 1 to many relationship with the queried table

Answer 3

This might be prohibitively expensive (perhaps only do it when a user inserts a new record?) but how about this:

for user in users:
  user-records = select * from records where user=user
  if user-records.length > 10:
    delete from records where user=user and date<user-records[10]

(in a mix of SQL and pseudocode)

Answer 4

I know this question is old, but the following SQLite statement will do what Rory was originally asking for in one statement - Delete all records for a given UserId that are not the 10 most recent records for that UserId (based on SomeDate).

DELETE FROM data
WHERE AnId IN (SELECT AnId
               FROM data AS d
               WHERE d.UserId = data.UserId
               ORDER BY SomeDate DESC
               LIMIT -1 OFFSET 10)

Answer 5

If you already haven't got the answer. If it's one table, then you don't need any joins. You can just use:

Delete From data
where AnId not in (Select AnId
                   from data
                   Order by SomeDate DESC
                   Limit 10)