Re: BUG #15882: Select .... UNION ALL

On Tuesday, July 2, 2019, PG Bug reporting form <noreply(at)postgresql(dot)org>
wrote:

> The following bug has been logged on the website:
>
> Bug reference: 15882
> Logged by: Vincenzo Campanella
> Email address: v(dot)campanella47(at)gmail(dot)com
> PostgreSQL version: 11.4
> Operating system: windows 10 build 1903
> Description:
>
> cSelect = "select 1 as prog,sum(imp_asl) as Importo_Asl,Count(Arc_Ref.n_
> Rif)
> as nRicette,sum(n_Pre) as nPrelievi " +
>
> "from " + MyFunc.cSchema + "Arc_Ref " +
>
> "where data >= '" + cAnno + "-01-01' and data <= '" + cAnno +
> "-01-31' and T_MPR='M' " +
>
> "union all " +
>
> "select 2 as prog,sum(imp_asl) as Importo_Asl,Count(Arc_Ref.n_Rif)
> as nRicette,sum(n_Pre) as nPrelievi " +
>
> "from " + MyFunc.cSchema + "Arc_Ref " +
>
> "where data >= '" + cAnno + "-02-01' and data <= '" + cAnno +
> "-02-" + MyFunc.Ultimo_Giorno_Mese(2, Converti.ToInt32(cAnno)) + "' and
> T_MPR='M' " +
> [...]

> This produces an unordered but random table.

unordered but random?

> I put the prog field and then make the ascending order on this field.
> In previous versions the order was in the typed sequence.
>

I too would expect the unioned rows to be produced in the order listed but
this is not bug because the only way PostgreSQL is required to maintain
record order in a query is if you specify an order by clause.

It occurs to me you are likely benefitting from the new parallel query
infrastructure here.

David J.