En SQLite, obtienes una columna de incremento automático usando INTEGER PRIMARY KEY
.(Y si confía en los valores reales de payers.id
en la consulta, debe proporcionarlas explícitamente).
No debe intentar anidar uniones cuando no es necesario:
SELECT payer_payment.payer_id,
Sum(payer_payment.amount) AS total_paid,
Sum(payer_payment.pays * payments_share.single_share) AS fair_share
FROM payers
INNER JOIN payer_payment
ON payers.id = payer_payment.payer_id
INNER JOIN (SELECT payment_id,
Sum(amount) / Sum(pays) AS single_share
FROM payer_payment
GROUP BY payment_id) AS payments_share
ON payer_payment.payment_id = payments_share.payment_id
WHERE payers.user_id = 1
GROUP BY payer_payment.payer_id;