Postgresql query GROUP BY not possible

Question

In my project I have this complex query:

SELECT FT."Riferimento1", FT."Riferimento2", "CodProdotto", "QuantitaFatturata", "PrezzoUnit", "DataFattura", "NumeroFattura", "CodCli"
FROM public.idocuments_as_fatturetestata FT
LEFT JOIN public.idocuments_as_fatturerighe FR ON FT."Riferimento1" = FR."Riferimento1" AND FT."Riferimento2" = FR."Riferimento2"
WHERE FT."CodCli" = '12192' GROUP BY "NumeroFattura";

If I don't use the GROUP BY option all was done but I have to grouping by NumeroFattura column.

When I add the Group BY sentence I get this error:

ERROR: column "ft.Riferimento1" must appear in the GROUP BY clause or be used in an aggregate function

if I add ft.Riferimento1 system ask me ft.Riferimento2 also and all columns, but I want to group just for NumeroFattura column.

"25"    "000006"    "191215002N"    1   1.800000    "2017-01-31 00:00:00+00"    589
"25"    "000009"    "112036402G"    100 0.970000    "2017-01-31 00:00:00+00"    318
"25"    "000009"    "213008200I"    200 1.660000    "2017-01-31 00:00:00+00"    318
"25"    "000009"    "213008200N"    150 1.660000    "2017-01-31 00:00:00+00"    318
"25"    "000009"    "213008500V1"   53.5    1.930000    "2017-01-31 00:00:00+00"    318
"25"    "000009"    "213008500E"    61  1.930000    "2017-01-31 00:00:00+00"    318
"25"    "000009"    "213008500R"    56  1.930000    "2017-01-31 00:00:00+00"    318
"25"    "000009"    "213008200G"    50  1.660000    "2017-01-31 00:00:00+00"    318
"25"    "000009"    "113066592N"    20  5.583000    "2017-01-31 00:00:00+00"    318
"25"    "000009"    "199900502N"    321 0.725000    "2017-01-31 00:00:00+00"    318
"25"    "000009"    "199900602N"    360 0.680000    "2017-01-31 00:00:00+00"    318
"25"    "000009"    "217001100F"    1200    2.036000    "2017-01-31 00:00:00+00"    318
"25"    "000009"    "112031102N"    1200    0.198000    "2017-01-31 00:00:00+00"    318
"25"    "000009"    "112044602N"    800 0.600000    "2017-01-31 00:00:00+00"    318
"25"    "000009"    "112036402N"    800 0.500000    "2017-01-31 00:00:00+00"    318
"25"    "000009"    "113066702N"    800 0.600000    "2017-01-31 00:00:00+00"    318
"25"    "000009"    "113066602N"    800 0.550000    "2017-01-31 00:00:00+00"    318
"25"    "000009"    "112530780N3"   5000    0.178000    "2017-01-31 00:00:00+00"    318

this is an example of output, in the last column i have the NumeroFattura row and i would to group for this value (in this example i should have two rows for results)

Someone can tell me why i can't group like i would?

So many thanks in advance

Answer 1

If you want one row per "NumeroFattura" , then use DISTINCT ON :

SELECT DISTINCT ON ("NumeroFattura") FT."Riferimento1", FT."Riferimento2",
       "CodProdotto", "QuantitaFatturata", "PrezzoUnit", "DataFattura",
       "NumeroFattura", "CodCli"
FROM public.idocuments_as_fatturetestata FT LEFT JOIN
     public.idocuments_as_fatturerighe FR
     ON FT."Riferimento1" = FR."Riferimento1" AND 
        FT."Riferimento2" = FR."Riferimento2"
WHERE FT."CodCli" = '12192' 
ORDER BY "NumeroFattura";

This returns an arbitrary matching row. It is unclear which row you want, but you can add an additional key to the ORDER BY to choose which of them.