Kreuztabelle mit einer großen oder undefinierten Anzahl von Kategorien

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')
;

Die Abfrage für die Katze:

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

Wenn die Anzahl der Wähler groß oder nicht bekannt ist, kann dies dynamisch erfolgen:

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; $do$;

Der obige Code erstellte den Tabellen-Pivot mit allen Entscheidungen:

select * from pivot where decision = 'Cat';