Krydstabeller med et stort eller udefineret antal kategorier

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')
;

Forespørgslen til 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

Hvis antallet af vælgere er stort eller ikke kendt, kan det gøres dynamisk:

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; $do$;

Ovenstående kode skabte tabellens pivot med alle beslutninger:

select * from pivot where decision = 'Cat';