如何在过去2年的Oracle中从表中选择10行

Question

I have a table that has close to 9 million+ rows from past 4 years I need to make a list close to 100 thousand samples from past 2 years. While doing so I can select X rows from each month starting July 2014.

    select distinct tb1.field
    from table1 tb1
    join table2 tb2 
    on tb.field = tb2.field
    where tb1.Date between to_date('1-July-2014','DD-MON-YYYY') and     to_date('8-Aug-2016','DD-MON-YYYY') 
    order by tb1.field

Thanks

Answer 1

If table tb1 has a column dt (I hope it's not called DATE, that is a reserved keyword and using it as a column name will most likely result in an error), and if you need, say, 100 purely random rows from each of the last 24 months, you could do something like this. Then you can join the result to other tables if you need to. I assume the other columns in tb1 (or the ones you need for the join) are col1, col2.

select col1, col2, dt
from (
        select col1, col2, dt, 
               row_number() over ( partition by trunc(dt, 'mm') 
                                   order by dbms_random.value() 
                                 ) as rn
        from   tb1
        where  dt between add_months(trunc(sysdate), -24) and sysdate
     )
where rn <= 100
;

Answer 2

Not sure how your SQL example is related to what you are asking for in English... But you can try something like this:

with q1 as ( select trunc(Date, 'month') mth, 
                    min(Date) start_dt, 
                    max(Date) end_dt
             from table1
             where date ...
             group by trunc(Date, 'month')),
     q2 as (select table1.*, 
                   row_number() over (partition by trunc(Date,'month') 
                                      order by [some random column]) seq
       where Date ... )
select q2.*
from q1 
join q2 
  on q2.Date between q1.start_dt and q1.end_dt 
     and q2.seq <= [x]