select
t1.name,
sum(case when t2.abbrev='foo' then t1.amount*t2.amount else 0 end) as foo,
sum(case when t2.abbrev='bar' then t1.amount*t2.amount else 0 end) as bar,
sum(case when t2.abbrev='baz' then t1.amount*t2.amount else 0 end) as baz
from usage t1 inner join points t2 on t1.points_id=t2.ident
group by t1.name;
SQL-Fiddle-Beispiel:http://sqlfiddle.com/#!15/cc84a/6;
Verwenden Sie die folgende PostgreSQL-Funktion für dynamische Fälle:
create or replace function sp_test()
returns void as
$$
declare cases character varying;
declare sql_statement text;
begin
select string_agg(concat('sum(case when t2.abbrev=','''',abbrev,'''',' then t1.amount*t2.amount else 0 end) as ', abbrev),',') into cases from points;
drop table if exists temp_data;
sql_statement=concat('create temporary table temp_data as select
t1.name,',cases ,'
from usage t1 inner join points t2 on t1.points_id=t2.ident
group by t1.name ');
execute sql_statement;
end;
$$
language 'plpgsql';
Funktion verwendet temporäre Tabelle zum Speichern dynamischer Spaltendaten.
Rufen Sie die Funktion auf folgende Weise auf, um Daten zu erhalten:
select * from sp_test(); select * from temp_data;
