The relatively new QuerySet.union operator has quite a few limitations:
[...] only LIMIT, OFFSET, COUNT(*), ORDER BY, and specifying columns (i.e.
> slicing, count(), order_by(), and values()/values_list()) are allowed on
> the resulting QuerySet. Further, databases place restrictions on what
> operations are allowed in the combined queries. For example, most databases
> don’t allow LIMIT or OFFSET in the combined queries.
>
I think most of these could be circumvented by having the combined queries
wrapped as subqueries, e.g.:
SELECT * FROM (
SELECT f1, f2 FROM t1 ORDER BY f2 OFFSET 10
)
UNION
SELECT * FROM (
SELECT f1, f2 FROM t2 ORDER BY f1 DESC LIMIT 3
)
As far as I know, all relevant databases support this workaround and there
isn't any performance penalty to it. Am I missing something?
— Thijs
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