Jeg har en tendens til at nærme mig denne type forespørgsel ved hjælp af betinget aggregering:
select ward,
max(case when seqnum = 1 then councillor end) as councillor1,
max(case when seqnum = 2 then councillor end) as councillor2,
max(case when seqnum = 3 then councillor end) as councillor3
from (select wc.*,
row_number() over (partition by ward order by councillor) as seqnum
from ward_councillors wc
) wc
group by ward;