Com base na descrição em sua pergunta e comentários, você deseja algo como:
case when start_date = next_day(trunc(start_date, 'MM') - 1, 'Sunday') -- date is on first sunday
then next_day(start_date, 'Sunday') -- next Sunday, which is second in month
else next_day(last_day(start_date), 'Sunday') -- first Sunday of next month
end
Com algumas datas de amostra em um CTE, incluindo algumas discutidas, mas também outras:
with cte (start_date) as (
select date '2018-05-30' from dual
union all select date '2018-06-01' from dual
union all select date '2018-06-02' from dual
union all select date '2018-06-03' from dual
union all select date '2018-06-04' from dual
union all select date '2018-06-30' from dual
union all select date '2018-07-01' from dual
union all select date '2018-07-02' from dual
union all select date '2018-07-03' from dual
union all select date '2018-07-04' from dual
union all select date '2018-07-05' from dual
union all select date '2018-07-06' from dual
union all select date '2018-07-07' from dual
union all select date '2018-07-08' from dual
union all select date '2018-07-31' from dual
union all select date '2018-08-01' from dual
union all select date '2018-08-02' from dual
union all select date '2018-08-03' from dual
union all select date '2018-08-04' from dual
union all select date '2018-08-05' from dual
union all select date '2018-08-06' from dual
)
select start_date,
to_char(start_date, 'Dy') as day,
case when to_char(start_date, 'Dy') = 'Sun'
then 'Yes' else 'No' end as is_sunday,
case when start_date = next_day(trunc(start_date, 'MM') - 1, 'Sunday')
then 'Yes' else 'No' end as is_first_sunday,
next_day(trunc(start_date, 'MM') - 1, 'Sunday') as first_sun_this_month,
next_day(trunc(start_date, 'MM') + 6, 'Sunday') as second_sun_this_month,
next_day(last_day(start_date), 'Sunday') as first_sun_next_month,
case when start_date = next_day(trunc(start_date, 'MM') - 1, 'Sunday') -- date is on first sunday
then next_day(start_date, 'Sunday') -- next Sunday, which is second in month
else next_day(last_day(start_date), 'Sunday') -- first Sunday of next month
end as result
from cte;
fica
START_DATE DAY IS_ IS_ FIRST_SUN_ SECOND_SUN FIRST_SUN_ RESULT
---------- ------------ --- --- ---------- ---------- ---------- ----------
2018-05-30 Wed No No 2018-05-06 2018-05-13 2018-06-03 2018-06-03
2018-06-01 Fri No No 2018-06-03 2018-06-10 2018-07-01 2018-07-01
2018-06-02 Sat No No 2018-06-03 2018-06-10 2018-07-01 2018-07-01
2018-06-03 Sun Yes Yes 2018-06-03 2018-06-10 2018-07-01 2018-06-10
2018-06-04 Mon No No 2018-06-03 2018-06-10 2018-07-01 2018-07-01
2018-06-30 Sat No No 2018-06-03 2018-06-10 2018-07-01 2018-07-01
2018-07-01 Sun Yes Yes 2018-07-01 2018-07-08 2018-08-05 2018-07-08
2018-07-02 Mon No No 2018-07-01 2018-07-08 2018-08-05 2018-08-05
2018-07-03 Tue No No 2018-07-01 2018-07-08 2018-08-05 2018-08-05
2018-07-04 Wed No No 2018-07-01 2018-07-08 2018-08-05 2018-08-05
2018-07-05 Thu No No 2018-07-01 2018-07-08 2018-08-05 2018-08-05
2018-07-06 Fri No No 2018-07-01 2018-07-08 2018-08-05 2018-08-05
2018-07-07 Sat No No 2018-07-01 2018-07-08 2018-08-05 2018-08-05
2018-07-08 Sun Yes No 2018-07-01 2018-07-08 2018-08-05 2018-08-05
2018-07-31 Tue No No 2018-07-01 2018-07-08 2018-08-05 2018-08-05
2018-08-01 Wed No No 2018-08-05 2018-08-12 2018-09-02 2018-09-02
2018-08-02 Thu No No 2018-08-05 2018-08-12 2018-09-02 2018-09-02
2018-08-03 Fri No No 2018-08-05 2018-08-12 2018-09-02 2018-09-02
2018-08-04 Sat No No 2018-08-05 2018-08-12 2018-09-02 2018-09-02
2018-08-05 Sun Yes Yes 2018-08-05 2018-08-12 2018-09-02 2018-08-12
2018-08-06 Mon No No 2018-08-05 2018-08-12 2018-09-02 2018-09-02
O
result coluna é a que você está interessado, as outras apenas tentam mostrar um pouco o funcionamento. Parece estranho ter as datas de resultado fora de sequência em comparação com as datas de entrada - 2018-06-03 indo para 2018--06-10, então as anteriores e depois vão para 2018-07-01. Mas parece ser isso que você quer.
