如何在超级查询中使用子查询的结果？

Question

I am trying to find the average age in a scenario of multiple tables. The problem is that age is a derived attribute calculated from date of birth. Now I have written the following query which has the age of all the people that meet the condition. Now I want to find the average age of all of these but I am not sure how to use the results of the sub-query in the super-query.

The query is:

Select  
    case
        when date(dob, '+' ||
            (strftime('%Y', 'now') - strftime('%Y', dob)) ||
            ' years') <= date('now')
        then strftime('%Y', 'now') - strftime('%Y', dob)
        else strftime('%Y', 'now') - strftime('%Y', dob) - 1
    end
    as age
from UserProfile where User_ID in
(Select User_ID from UserProfile
where User_ID IN
(Select Channel_ID
from Channels
where Channel_Type = 'Public-Channel'
group by Channel_ID
HAVING (SUM(LENGTH(Video_IDs) - LENGTH(REPLACE(Video_IDs, ',', '')) + 1)) > 4));

And the output is a one column list of all ages, can you tell me how to calculate the average age because that's the only thing I want to display.

Answer 1

If I understand correctly, you just want one simple number as the end result. You can just go up one more level to find the average age.

SELECT avg(age) FROM (
Select  
    case
        when date(dob, '+' ||
            (strftime('%Y', 'now') - strftime('%Y', dob)) ||
             ' years') <= date('now')
         then strftime('%Y', 'now') - strftime('%Y', dob)
         else strftime('%Y', 'now') - strftime('%Y', dob) - 1
     end
     as age
 from UserProfile where User_ID in
 (Select User_ID from UserProfile
 where User_ID IN
 (Select Channel_ID
from Channels
  where Channel_Type = 'Public-Channel'
 group by Channel_ID
 HAVING (SUM(LENGTH(Video_IDs) - LENGTH(REPLACE(Video_IDs, ',', '')) +      1)) > 4)))