Hi,
I need to show a moving statistic of states of objects for every month
since beginning of 2013.
There are tables like
objects ( id integer, name text );
state ( id integer, state text ); 10=A, 20=B ... 60=F
history ( object_id integer, state_id, ts timestamp );
Every event that changes the state of an object is recorded in the
history table.
I need to count the numbers of As, Bs, ... on the end of month.
The subquery x finds the last state before a given date, here february 1st.
select s.status, count(*)
from ( select distinct on ( object_id ) status_id from history where
ts < '2013/02/01' order by object_id, ts desc ) as x join status as
s on x.status_id = s.id
group by s.status
order by s.status;
Now I need this for a series of months.
This would give me the relevant dates.
select generate_series ( '2013/02/01'::date, current_date + interval '1
month', interval '1 month' )
How could I combine those 2 queries so that the date in query 1 would be
replaced dynamically with the result of the series?
To make it utterly perfect the final query should show a crosstab with
the states as columns.
It is possible that in some months not every state exists so in this
case the crosstab-cell should show a 0.
Month A B C ...
2013/02/01
2013/03/01
...