Is there an sql query to count the number of people in a particular year, knowing the date of birth and the date of death of each person? - sql

Question

I have a table showing the name, the date of birth and the date of death of people (1900-2000). I need to know the number of people for each year in a certain period of time, for example, in 1940 the population was 2.3 billion, in 1941 2.4 billion, in 1942 2.2 billion and so on until 1950.
I work in SAS Enterprise Guide and maybe the code will look a little different than normal sql. At least I want to see something like this:
~
count of people | year
2.300.000.000 |1940
2.400.000.000 |1941
.....................
select
count(name),
from db
where bd<1jan1940 and dd>=1jan1940 and dd=<31dec1940
group by month

Answer 1

First of all, you must know the initial population at the end of 1899. Let's say that was 2 billion. Then add births minus deaths for each year. (You must access the table twice in order to do this, once for births and once for deaths.) Use SUM OVER to get a running total.
I am not sure which DBMS you are actually using, but this is pretty standard SQL:
select yr, 2000000000 + sum(births.cnt - deaths.cnt) over (order by yr)
from
(
select extract(year from bd) as yr, count(*) as cnt
from db
group by extract(year from bd)
) births
join
(
select extract(year from dd) as yr, count(*) as cnt
from db
group by extract(year from dd)
) deaths using (yr)
order by yr;

Answer 2

data dob_data;
do i = 1 to 10000;
num = ceil(rand('UNIFORM',0,10));
dob = intnx('day','01JAN1899'd,ceil(rand('UNIFORM',1,36865)));
select (num);
when (1) dod = intnx('day',dob,ceil(rand('UNIFORM',1,36865)));
otherwise dod = .;
end;
output;
end;
format dob dod date9.;
drop num;
run;
data calendar;
do i=0 to 100;
year = 1900+i;
soy = intnx('year','01JAN1900'd,i,'s');
eoy = intnx('year','01JAN1900'd,i,'e');
output;
end;
format soy eoy date9.;
run;
proc sql;
create table pop as
select year,
sum(case when DOB < soy and coalesce(DOD,'31DEC2200'd) ge soy then 1 else 0 end) as Alive_At_Start,
sum(case when DOB between soy and eoy then 1 else 0 end) as Born_During,
sum(case when coalesce(DOD,'31DEC2200'd) between soy and eoy then -1 else 0 end) as Passed,
sum(case when DOB le eoy and coalesce(DOD,'31DEC2200'd) > eoy then 1 else 0 end) as Alive_At_End
from dob_data t1, calendar t2
group by year;
quit;