¿Consulta PostgreSQL para seleccionar datos de la semana pasada?

Esta condición devolverá registros desde el domingo hasta el sábado de la semana pasada:

WHERE created BETWEEN
    NOW()::DATE-EXTRACT(DOW FROM NOW())::INTEGER-7 
    AND NOW()::DATE-EXTRACT(DOW from NOW())::INTEGER

Hay un ejemplo:

WITH compras AS (
    SELECT ( NOW() + (s::TEXT || ' day')::INTERVAL )::TIMESTAMP(0) AS created
    FROM generate_series(-20, 20, 1) AS s
)
SELECT to_char( created, 'DY'::TEXT), created
FROM compras
WHERE created BETWEEN
    NOW()::DATE-EXTRACT(DOW FROM NOW())::INTEGER-7 
    AND NOW()::DATE-EXTRACT(DOW from NOW())::INTEGER

En respuesta a @d456:

Así es, BETWEEN incluye la medianoche del domingo en ambos extremos del intervalo. Para excluir la medianoche del domingo al final del intervalo, es necesario utilizar los operadores >= y < :

WITH compras AS (
    SELECT s as created
    FROM generate_series( -- this would produce timestamps with 20 minutes step
             (now() - '20 days'::interval)::date,
             (now() + '20 days'::interval)::date,
             '20 minutes'::interval) AS s
)
SELECT to_char( created, 'DY'::TEXT), created
FROM compras
WHERE TRUE
    AND created >= NOW()::DATE-EXTRACT(DOW FROM NOW())::INTEGER-7
    AND created <  NOW()::DATE-EXTRACT(DOW from NOW())::INTEGER