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')
;
Frågan för katten:
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
Om antalet väljare är stort eller inte känt så kan det göras dynamiskt:
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; $do$;
Ovanstående kod skapade tabellpivoten med alla beslut:
select * from pivot where decision = 'Cat';