oracle - SQL to Find Number of Weeks an Employee Was Active Between Two Dates -

i have table list of dates employee became active/inactive , want count weeks employee active within date range.

so table (ps_job) have values this:

emplid     effdt       hr_status ------     -----       ------ 1000       01-jul-11   1000       01-sep-11   1000       01-jan-12   1000       01-mar-12   1000       01-sep-12   

the query need show me number of weeks emplid active 01-jul-11 31-dec-12.

the desired result set be:

emplid     weeks_active ------     ------------ 1000       35 

i got number 35 adding results sqls below:

select (next_day('01-sep-11','sunday') - next_day('01-jul-11','sunday'))/7 weeks_active dual; select (next_day('01-mar-12','sunday') - next_day('01-jan-12','sunday'))/7 weeks_active dual; select (next_day('31-dec-12','sunday') - next_day('01-sep-12','sunday'))/7 weeks_active dual; 

the problem can't seem figure out how create single query statement go through rows every employee within date range , return each emplid , number of weeks active. prefer use basic sql instead of pl/sql can transfer peoplesoft query can run user, willing run user using oracle sql developer if need be.

database: oracle database 11g enterprise edition release 11.2.0.3.0 - 64bit production

here i'm using lead in subquery next date , summing intervals in outer query:

with q (     select emplid, effdt, hr_status         , lead (effdt, 1) on (partition emplid order effdt) next_effdt     ps_job     order emplid, effdt ) select emplid     , trunc(sum((trunc(coalesce(next_effdt, current_timestamp)) - trunc(effdt)) / 7)) weeks_active q hr_status = 'a' group emplid; 

the coalesce function grab system date in event cannot find matching i record (employee current). substitute end of year if that's spec.

note i'm not doing rigorous testing see entries ordered a/i/a/i etc., might want add checks of nature if know data requires it.

feel free play @ sql fiddle.