How I can select random amount of rows based on varios criterias?

I have a table that has 3 main categories: age, city and gender.

The gender column is boolean.

The age category is in the following range:

['18-25','26-35','36-45','46-55','56-65','66-75','75+']

The city category has around 19 cities. So, for each city in category '18-25' and '75+' I would like to select 24 random rows for females and 20 for males.

For the rest of the cities, I would like to select 40 random males and 47 random females.

Is it possible to achieve this without having to run a specific query for each case?

I’m sorry the lack of code, but honestly I don’t even know where or how to start 🙁

Answer

You can use row_number() to enumerate the rows randomly and then just filter:

select t.*
from (select t.*,
             row_number() over (partition by city, age, gender order by rand()) as seqnum
      from t
     ) t
where (age in ('18-25', '75+') and
       (gender = 'female' and seqnum <= 24 or
        gender = 'male' and seqnum <= 20
       )
      ) or 
      (age not in ('18-25', '75+') and
       (gender = 'female' and seqnum <= 47 or
        gender = 'male' and seqnum <= 40
       )
      )