Hi, I am trying to use a correlated subquery with an 'order by random() limit 2' to pick upto two random rows for each value in the outer query. I am not sure if I am doing this correctly, but the number of rows I am getting seems to vary randomly which doesn't make sense to me. If i replace the order by random() with order by product I always get the expected number of rows. I have tried to create a simplified version of the code below to replicate the issue.
I am experiencing the problem on sqlite 3.22.0, but I have tried on
sqliteonline.com which I think is using 3.27.2 and am seeing similar results.
Thanks,
Kevin
---
create table if not exists test_productattribs (product text primary key, attr,
val);
insert or ignore into test_productattribs values
('1', 'area', 'a'),
('2', 'area', 'b'),
('3', 'area', 'a'),
('4', 'area', 'a')
;
--In the real query, this is done inside the with, but it does not seem
relevant
--to the issue.
create table if not exists
test_productarea
as select
product,
val as area
from
test_productattribs
where
attr='area'
;
--I have two areas, 'a' and 'b'. I limit to two random products from each area
--As area 'b' only has one product, I always expect to get 3 rows, 1 for area
'b', and 2 for
--area 'a'.
with
dareas as (select distinct
area
from
test_productarea)
select
da.area,
pa.product
from
dareas as da
left join test_productarea as pa
--if I don't order by random, but instead by product, I always get the
correct number of rows
on pa.product in (select product from test_productarea where da.area=area
order by random() limit 2)
-- In the real query, this order by is required to see a different number of
rows to the number in the
-- limit. However, it seems it is not required in the small test dataset.
-- order by
-- da.area,
-- pa.product
;
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