id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
36096	QuerySet.values() on a UNION query results in a broken query	Isaac Nygaard		"When calling `QuerySet.values()` on a union query, I get some internal Django errors. For example:

{{{
qs = model.values(*grouping).annotate(**annotations)

// SAMPLE A: the following raises internal Django errors
t1 = qs.annotate(time_period=Value(1)).filter(filter_1)
t2 = qs.annotate(time_period=Value(2)).filter(filter_2)
qs = t1.union(t2).values(*values)

// SAMPLE B: the following works
t1 = qs.annotate(time_period=Value(1)).filter(filter_1).values(*values)
t2 = qs.annotate(time_period=Value(2)).filter(filter_2).values(*values)
qs = t1.union(t2)
}}}

Sample A fails because `qs.annotation_select` becomes different from `t1.annotation_select` and `t2.annotation_select`. Django doesn't complain until the query is run, and the database returns different columns (or columns in a different order) than what it was expecting.

I would think Django should do one of the following:
1. have `qs.values()` update the selected annotations for its two child combinator queries, t1/t2 (this is what I expected and why I wrote the code that way)
2. disallow `values()` on union queries, e.g. by raising an informative error
3. detect that `qs.annotation_select` columns do not match `annotation_select` of the two child combinator queries and raise an informative error"	Uncategorized	closed	Database layer (models, ORM)	5.0	Normal	invalid		Simon Charette	Unreviewed	0	0	0	0	0	0