create table vote (Photo integer, Voter text, Decision text);
insert into vote values
(1, 'Alex', 'Cat'),
(1, 'Bob', 'Dog'),
(1, 'Carol', 'Cat'),
(1, 'Dave', 'Cat'),
(1, 'Ed', 'Cat'),
(2, 'Alex', 'Cat'),
(2, 'Bob', 'Dog'),
(2, 'Carol', 'Cat'),
(2, 'Dave', 'Cat'),
(2, 'Ed', 'Dog'),
(3, 'Alex', 'Horse'),
(3, 'Bob', 'Horse'),
(3, 'Carol', 'Dog'),
(3, 'Dave', 'Horse'),
(3, 'Ed', 'Horse'),
(4, 'Alex', 'Horse'),
(4, 'Bob', 'Horse'),
(4, 'Carol', 'Cat'),
(4, 'Dave', 'Horse'),
(4, 'Ed', 'Horse'),
(5, 'Alex', 'Dog'),
(5, 'Bob', 'Cat'),
(5, 'Carol', 'Cat'),
(5, 'Dave', 'Cat'),
(5, 'Ed', 'Cat')
;
Заявката за котката:
select photo,
alex + bob + carol + dave + ed as Total,
alex, bob, carol, dave, ed
from crosstab($$
select
photo, voter,
case decision when 'Cat' then 1 else 0 end
from vote
order by photo
$$,'
select distinct voter
from vote
order by voter
'
) as (
photo integer,
Alex integer,
Bob integer,
Carol integer,
Dave integer,
Ed integer
);
photo | total | alex | bob | carol | dave | ed
-------+-------+------+-----+-------+------+----
1 | 4 | 1 | 0 | 1 | 1 | 1
2 | 3 | 1 | 0 | 1 | 1 | 0
3 | 0 | 0 | 0 | 0 | 0 | 0
4 | 1 | 0 | 0 | 1 | 0 | 0
5 | 4 | 0 | 1 | 1 | 1 | 1
Ако броят на гласоподавателите е голям или не е известен, това може да се направи динамично:
do $do$
declare
voter_list text;
r record;
begin
drop table if exists pivot;
voter_list := (
select string_agg(distinct voter, ' ' order by voter) from vote
);
execute(format('
create table pivot (
decision text,
photo integer,
Total integer,
%1$s
)', (replace(voter_list, ' ', ' integer, ') || ' integer')
));
for r in
select distinct decision from vote
loop
execute (format($f$
insert into pivot
select
%3$L as decision,
photo,
%1$s as Total,
%2$s
from crosstab($ct$
select
photo, voter,
case decision when %3$L then 1 else 0 end
from vote
order by photo
$ct$,$ct$
select distinct voter
from vote
order by voter
$ct$
) as (
photo integer,
%4$s
);$f$,
replace(voter_list, ' ', ' + '),
replace(voter_list, ' ', ', '),
r.decision,
replace(voter_list, ' ', ' integer, ') || ' integer'
));
end loop;
end; $do$;
Горният код създаде опорната точка на таблицата с всички решения:
select * from pivot where decision = 'Cat';