Fields placed at the SELECT clause in an erroneous order.

[Thodoris Sotiropoulos]

I have a query of the form (simplified for opening issue)

q1 = Model.objects.values('col_a', 'col_b')
q2 = Model.objects.annotate(col_c=F('col_a')).values('col_c', 'col_b')
q1.union(q2)

The generated SQL query is

SELECT "model"."col_a", "model"."col_b" FROM "model" UNION SELECT "model"."col_b", "model"."col_a" AS "col_c" FROM "model"

It seems to me that when inspecting the second sub-query, django does not place fields at the SELECT clause in the correct order, that is

SELECT "model"."col_b", "model"."col_a" AS "col_c"

instead of

SELECT  "model"."col_a" AS "col_c", "model"."col_b"

[Mariusz Felisiak]

This by design, annotation are always at the end. It doesn't cause any issue in your example.

[Thodoris Sotiropoulos]

Ah OK, thanks.

There is actually an issue in this example, because columns of the two sub-queries are not combined correctly.
Column 'col_c' (of the second sub-query) is combined with the column 'column_b' (of the first sub-query), and not column 'column_a' as intended.

[Mariusz Felisiak]

Ahh Yes, sorry I missed union(), so it's a duplicate of #28553.