Qfyilyi

I would like to select the following segment.

Random 5500 rows including the following segments:

       Subcategorie (sex): - 3300 men

                           - 2200 women

              Subcategorie (age): - 2140 between 18-34 years

                                  - 2100 between 35-54 years

                                  - 1260 between 55-99 years

How could I solve this in a select statement?

The problem is, you use the word "random" but you have a very precise break down of cohorts by age and sex. A truly random single query won't produce such exact quotas. So your query must necessarily be complicated: you need to divide the whole table into subsets which meet your constraints then randomly select from those subsets. Something like this...

select * from (

   select * from whatever

   where sex = 'M'

   and age between 18 and 34

   order by dbms_random.value 

)

where rownum <= 1284

union all

select * from (

   select * from whatever

   where sex = 'M'

   and age between 35 and 54

   order by dbms_random.value 

)

where rownum <= 1260

union all    select * from (

   select * from whatever

   where sex = 'M'

   and age between 55 and 99

   order by dbms_random.value 

)

where rownum <= 756

union all

select * from (

   select * from whatever

   where sex = 'F'

   and age between 18 and 34

   order by dbms_random.value 

)

where rownum <= 856

union all

select * from (

   select * from whatever

   where sex = 'F'

   and age between 35 and 54

   order by dbms_random.value 

)

where rownum <= 840

union all    select * from (

   select * from whatever

   where sex = 'F'

   and age between 55 and 99

   order by dbms_random.value 

)

where rownum <= 504

This may perform poorly, depending on the usual factors - size of table, indexing, etc - but it will produce those exact cohorts.

In case it's not obvious, the rownum bounds are the number of hits in each age group multiplied by the ratio of men to women (3:2).