Thread: Sorting aggregate column contents
Is it possible to sort the content of an aggregate text column? Query: select s.name, ag_concat(c.name) from state s inner join city c on (c.idstate = s.idstate) group by s.name order by s.name; Result: name | ag_concat -------+--------------------------- RS | Porto Alegre, Gramado SP | Osasco (2 rows) Expected result: name | ag_concat -------+--------------------------- RS | Gramado, Porto Alegre SP | Osasco (2 rows) I tried "order by s.name, c.name" but it causes a error: ERROR: column "c.name" must appear in the GROUP BY clause or be used in an aggregate My function and aggregate code: CREATE FUNCTION f_concat (text, text) RETURNS text AS $$ DECLARE t text; BEGIN IF character_length($1) > 0 THEN t = $1 || ', ' || $2; ELSE t = $2; END IF; RETURN t; END; $$ LANGUAGE plpgsql; CREATE AGGREGATE ag_concat ( sfunc = f_concat, basetype = text, stype = text, initcond = '' ); -- Everton
On May 02 06:00, Everton Luís Berz wrote: > Is it possible to sort the content of an aggregate text column? > > Query: > select s.name, ag_concat(c.name) from state s > inner join city c on (c.idstate = s.idstate) > group by s.name > order by s.name; IMHO, you can receive results ordered by using a subselect: SELECT T.s_name, ag_concat(T.c_name) FROM (SELECT s.name, c.name FROM state AS s INNER JOIN city AS c ON(c.idstate = s.idstate) ORDER BY s.name, c.name) AS T (s_name, c_name) GROUP BY T.s_name; Regards.
On Wed, May 03, 2006 at 00:13:40 +0300, Volkan YAZICI <yazicivo@ttnet.net.tr> wrote: > On May 02 06:00, Everton Luís Berz wrote: > > Is it possible to sort the content of an aggregate text column? > > > > Query: > > select s.name, ag_concat(c.name) from state s > > inner join city c on (c.idstate = s.idstate) > > group by s.name > > order by s.name; > > IMHO, you can receive results ordered by using a subselect: > > SELECT T.s_name, ag_concat(T.c_name) > FROM (SELECT s.name, c.name > FROM state AS s > INNER JOIN city AS c ON (c.idstate = s.idstate) > ORDER BY s.name, c.name) AS T (s_name, c_name) > GROUP BY T.s_name; Note that this is nonstandard, but is an intentional (but I am not sure if it's documented) feature of Postgres. There can be some similar situations where you need to use OFFSET 0 to prevent optimizations that will break the ordering.
It works fine. But I wouldn't like using subselect's, then if somebody elseknows about an operator or something like thatto put on the aggregator, please tell me. Volkan YAZICI escreveu: > On May 02 06:00, Everton Luís Berz wrote: > >> Is it possible to sort the content of an aggregate text column? >> >> Query: >> select s.name, ag_concat(c.name) from state s >> inner join city c on (c.idstate = s.idstate) >> group by s.name >> order by s.name; >> > > IMHO, you can receive results ordered by using a subselect: > > SELECT T.s_name, ag_concat(T.c_name) > FROM (SELECT s.name, c.name > FROM state AS s > INNER JOIN city AS c ON (c.idstate = s.idstate) > ORDER BY s.name, c.name) AS T (s_name, c_name) > GROUP BY T.s_name; > > > Regards. > >
> It works fine. But I wouldn't like using subselect's, then if somebody else > knows about an operator or something like that to put on the aggregator, > please tell me. I think the nature of the f_concat makes it difficult to sort, since it simply adds the next value, so if the source table gives value in the order of 'a','c','d','b' there's no way to handle them within f_concat unless you modify and rearrange the previous result string from within f_concat. So the source table (city) should be sorted. I don't know if this is a standard way, but this one seems to do that. ====================================================== select s.name, ag_concat(c.name) from state s inner join (select * from city order by name desc) as c on c.idstate=s.idstate group by s.name order by 1; OR select s.name, ag_concat(c.name) from state s, (select * from city order by name desc) as c where c.idstate = s.idstate group by s.name order by 1; ====================================================== I'm just reordering the source table on the fly. Curiously, if you don't have 'desc' you'll get a reverse ordered list. (z,...,a) I think your needs may also be met without any aggregator as well (there may be marginal cases which I haven't thought of, but I assume they can be handled if needed) ====================================================== select s.name, array_to_string(array(select name from city where idstate = s.idstate order by name),',') from state s; ====================================================== name | array_to_string ------+--------------------- RP | Gramado,Port Alegre SP | Osasco * I see normalization issue here but guess it's not important. Regards, Ben K. Developer http://benix.tamu.edu
Thanks a lot the explanation.
I tested all cases and I noticed that reordering the source table (city)
not works on all cases, so I think Postgresql perform different internal
sort to optimize some query's.
I noticed this in other query I performed:
select s.ano, s.semestre, dhc.iddisciplinahorariocurriculo, count(*),
ag_concatenar_com_quebra_de_linha(td.turno)AS turno from disciplinahorariocurriculo dhc
inner join horariocurriculo hc on (hc.idhorariocurriculo =
dhc.idhorariocurriculo)
inner join semestre s on (s.idsemestre = hc.idsemestre)
inner join (select tdinterno.iddisciplinahorariocurriculo, t.turno from
turnodisciplina tdinterno inner join turno t on (t.idturno = tdinterno.idturno) order by
tdinterno.iddisciplinahorariocurriculo,t.turno) as
td on (td.iddisciplinahorariocurriculo = dhc.iddisciplinahorariocurriculo)
-- where dhc.iddisciplinahorariocurriculo = 8282 group by 1, 2, 3 having count(*) > 1 order by 1, 2, 3;
ano | semestre | iddisciplinahorariocurriculo | count | turno
... 2004 | 2 | 8282 | 3 | 23, 63, 43
^ ^ ^
...
If I remove the comment in the 'where' line there is the right result: ano | semestre | iddisciplinahorariocurriculo |
count| turno
------+----------+------------------------------+-------+------------ 2004 | 2 | 8282 |
3 | 23, 43, 63 ^ ^ ^
(1 row)
I didn't know the array_to_string way, I think I will use it. It's safe
and easy.
Regards,
--
Everton
Ben K. escreveu:
>> It works fine. But I wouldn't like using subselect's, then if somebody
>> else
>> knows about an operator or something like that to put on the
>> aggregator, please tell me.
>
>
>
> I think the nature of the f_concat makes it difficult to sort, since it
> simply adds the next value, so if the source table gives value in the
> order of 'a','c','d','b' there's no way to handle them within f_concat
> unless you modify and rearrange the previous result string from within
> f_concat.
>
>
> So the source table (city) should be sorted. I don't know if this is a
> standard way, but this one seems to do that.
>
>
> ======================================================
> select s.name, ag_concat(c.name) from state s inner join (select * from
> city order by name desc) as c on c.idstate=s.idstate group by s.name
> order by 1;
>
> OR
>
> select s.name, ag_concat(c.name) from state s, (select * from city order
> by name desc) as c where c.idstate = s.idstate group by s.name order by 1;
> ======================================================
>
>
> I'm just reordering the source table on the fly. Curiously, if you don't
> have 'desc' you'll get a reverse ordered list. (z,...,a)
>
> I think your needs may also be met without any aggregator as well (there
> may be marginal cases which I haven't thought of, but I assume they can
> be handled if needed)
>
> ======================================================
> select s.name, array_to_string(array(select name from city where idstate
> = s.idstate order by name),',') from state s;
> ======================================================
>
> name | array_to_string
> ------+---------------------
> RP | Gramado,Port Alegre
> SP | Osasco
>
>
> * I see normalization issue here but guess it's not important.
>
>
>
> Regards,
>
> Ben K.
> Developer
> http://benix.tamu.edu
>
People from brazilian postgresql list sent me another way to sort the column contents. The way is the aggregate accumulate values and after run an array sort function. It worked fine. I think the subquery in function f_select_array does not decrease performance. Follow the code: --from http://archives.postgresql.org/pgsql-general/2005-12/msg01093.php CREATE FUNCTION f_select_array(anyarray) RETURNS SETOF anyelement AS $$ BEGIN FOR i IN array_lower($1, 1) .. array_upper($1, 1) LOOP RETURN NEXT $1[i]; END LOOP; RETURN; END; $$ LANGUAGE plpgsql IMMUTABLE STRICT; CREATE FUNCTION f_sort_array(anyarray) RETURNS anyarray AS $$ SELECT array(SELECT * FROM f_select_array($1) ORDER BY 1) $$ LANGUAGE sql IMMUTABLE STRICT; -- from http://www.postgresql.org/docs/8.1/interactive/xaggr.html CREATE AGGREGATE ag_accum ( sfunc = array_append, basetype = anyelement, stype = anyarray, initcond = '{}' ); select e.sigla, array_to_string(f_sort_array(ag_accum(m.nome)), ', ') AS municipio from estado e inner join municipio m on (m.idestado = e.idestado) group by e.sigla order by e.sigla; /* result */ sigla | municipio -------+----------------------- RS | Gramado, Porto Alegre SP | Osasco (2 rows) -- Everton On 5/3/06, Everton Luís Berz <everton.berz@gmail.com> wrote: > Thanks a lot the explanation. > > I tested all cases and I noticed that reordering the source table (city) > not works on all cases, so I think Postgresql perform different internal > sort to optimize some query's. > I noticed this in other query I performed: > > select s.ano, > s.semestre, > dhc.iddisciplinahorariocurriculo, > count(*), > ag_concatenar_com_quebra_de_linha(td.turno) AS turno > from disciplinahorariocurriculo dhc > inner join horariocurriculo hc on (hc.idhorariocurriculo = > dhc.idhorariocurriculo) > inner join semestre s on (s.idsemestre = hc.idsemestre) > inner join (select tdinterno.iddisciplinahorariocurriculo, t.turno from > turnodisciplina tdinterno > inner join turno t on (t.idturno = tdinterno.idturno) > order by tdinterno.iddisciplinahorariocurriculo, t.turno) as > td on (td.iddisciplinahorariocurriculo = dhc.iddisciplinahorariocurriculo) > -- where dhc.iddisciplinahorariocurriculo = 8282 > group by 1, 2, 3 > having count(*) > 1 > order by 1, 2, 3; > > ano | semestre | iddisciplinahorariocurriculo | count | turno > ... > 2004 | 2 | 8282 | 3 | 23, 63, 43 > ^ ^ ^ > ... > > If I remove the comment in the 'where' line there is the right result: > ano | semestre | iddisciplinahorariocurriculo | count | turno > ------+----------+------------------------------+-------+------------ > 2004 | 2 | 8282 | 3 | 23, 43, 63 > ^ ^ ^ > (1 row) > > > I didn't know the array_to_string way, I think I will use it. It's safe > and easy. > > Regards, > -- > Everton > > > Ben K. escreveu: > >> It works fine. But I wouldn't like using subselect's, then if somebody > >> else > >> knows about an operator or something like that to put on the > >> aggregator, please tell me. > > > > > > > > I think the nature of the f_concat makes it difficult to sort, since it > > simply adds the next value, so if the source table gives value in the > > order of 'a','c','d','b' there's no way to handle them within f_concat > > unless you modify and rearrange the previous result string from within > > f_concat. > > > > > > So the source table (city) should be sorted. I don't know if this is a > > standard way, but this one seems to do that. > > > > > > ====================================================== > > select s.name, ag_concat(c.name) from state s inner join (select * from > > city order by name desc) as c on c.idstate=s.idstate group by s.name > > order by 1; > > > > OR > > > > select s.name, ag_concat(c.name) from state s, (select * from city order > > by name desc) as c where c.idstate = s.idstate group by s.name order by 1; > > ====================================================== > > > > > > I'm just reordering the source table on the fly. Curiously, if you don't > > have 'desc' you'll get a reverse ordered list. (z,...,a) > > > > I think your needs may also be met without any aggregator as well (there > > may be marginal cases which I haven't thought of, but I assume they can > > be handled if needed) > > > > ====================================================== > > select s.name, array_to_string(array(select name from city where idstate > > = s.idstate order by name),',') from state s; > > ====================================================== > > > > name | array_to_string > > ------+--------------------- > > RP | Gramado,Port Alegre > > SP | Osasco > > > > > > * I see normalization issue here but guess it's not important. > > > > > > > > Regards, > > > > Ben K. > > Developer > > http://benix.tamu.edu > > > -- Everton