Pl/SQL and building out monthly data from Start and Stop Dates - oracle

Question

PL/SQL is not my strong suite. I am decent with SQL, but I have a challenge that I could really use your help with, if possible. I am using SQL Developer, if that helps.
I have a table that is a join from two other tables, but suffice it to say, it has the following applicaple columns:
FTE_NAME (VARCHAR2)
PRIMARY_BILLALBE_ROLE (VARCHAR2)
INVOICABLE_ALLOCATION (NUMBER)
CONTRACTED_FTE (NUMBER)
FTE_COUNTRY (VARCHAR2)
BILLING_START_DATE (DATE)
BILLING_END_DATE (DATE)
Here is an example of what I am trying to do:
I have actually done this using VBA and excel and it works great, but now the data is on an Oracle Server and its time for an update.
Example Rows:
| FTE_NAME | PRIMARY_BILLABLE_ROLE | INVOICEABLE_ALLOCATION | CONTRACTED_FTE | FTE_COUNTRY | BILLING_START_DATE | BILLING_END_DATE |
|------------|-----------------------|------------------------|----------------|-------------|--------------------|------------------|
| John Smith | Associate Manager | 1 | 1 | USA | January, 01 2013 | May, 01 2013 |
| John Smith | Manager | 1 | 1 | USA | May, 02 2013 | (null) |
What I would need to happen is that the PL/SQL code would build a monthly table and row by row include or exclude the row in that month, so from 01-JAN-2013 to 05-MAY-2013, the monthly table might look like this now with a MONTH COLUMN up front:
| MONTHLY | FTE_NAME | PRIMARY_BILLABLE_ROLE | INVOICEABLE_ALLOCATION | CONTRACTED_FTE | FTE_COUNTRY | BILLING_START_DATE | BILLING_END_DATE |
|-------------------|------------|-----------------------|------------------------|----------------|-------------|--------------------|------------------|
| January, 01 2013 | John Smith | Associate Manager | 1 | 1 | USA | January, 01 2013 | May, 01 2013 |
| February, 01 2013 | John Smith | Associate Manager | 1 | 1 | USA | January, 01 2013 | May, 01 2013 |
| March, 01 2013 | John Smith | Associate Manager | 1 | 1 | USA | January, 01 2013 | May, 01 2013 |
| April, 01 2013 | John Smith | Associate Manager | 1 | 1 | USA | January, 01 2013 | May, 01 2013 |
| May, 01 2013 | John Smith | Associate Manager | 1 | 1 | USA | January, 01 2013 | May, 01 2013 |
| May, 01 2013 | John Smith | Manager | 1 | 1 | USA | May, 02 2013 | (null) |
The lines for MAY would both be included in the 01-MAY-2013 rows, because that manager still worked as an Associate Manager for those few days. I used the start and end dates to calculate how many days.
The big part I need help with is how to get the table to build with a MONTHLY column using the first day of the month. There will 1000s of lines and each building everyday. I would have this code running in a view which will feed report and dashboards.
I really appreciate any help you can provide.
David

Answer 1

You can populate desired dates from scratch like in this example query:
with report_params as (
-- just to introduce variables
select
2013 year_value,
4 start_month,
6 end_month
from dual
),
report_months as (
-- list of first dates of all required months
select
add_months( -- add months to
trunc( -- January, 1st of year from parameters
to_date(
(select year_value from report_params),
'yyyy'
),
'yyyy'
),
(select start_month from report_params) + level - 2
)
from
dual
connect by
-- select number of rows (levels) from start_month to end_month
level <= (select end_month - start_month + 1 from report_params)
)
select * from report_months;
Another possibility is to analyze a table and generate diapason between minimum and maximum values:
with bound_months as (
select
min(trunc(billing_start_date,'mm')) as first_month,
max(trunc(billing_start_date,'mm')) as last_month
from
applicable_columns
),
report_months as (
select
add_months(
(select first_month from bound_months),
level - 1
)
as first_date
from
dual
connect by
-- select number of rows (levels) from start_month to end_month
level <= (select months_between(last_month,first_month)+1 from bound_months)
)
select * from report_months;
After that you can join list of months to data table/view with applicable columns:
with bound_months as (
select
min(trunc(billing_start_date,'mm')) as first_month,
max(trunc(billing_start_date,'mm')) as last_month
from
applicable_columns
),
report_months as (
select
add_months(
(select first_month from bound_months),
level - 1
)
as first_date
from
dual
connect by
-- select number of rows (levels) from start_month to end_month
level <= (select months_between(last_month,first_month)+1 from bound_months)
)
select
months.first_date,
data.*
from
report_months months,
applicable_columns data
where
data.billing_start_date < add_months(months.first_date,1)
and
nvl(data.billing_end_date, months.first_date) >= months.first_date
order by
first_date, fte_name, primary_billable_role
SQLFiddle test