Generate timespans that can used in place of UNIONs when working with dates.

Timespans.sql

/*
Author:   Craig Buchanan
Purpose:  Generate timespans (date ranges); timespans are aligned with monthly boundaries
Parameters:
  :periods - number of timespans to generate
  :length - length of each timespan, in months
  :offset - spacing between timespans, in months
  :ending_on - the most-recent timespan should end on this date; supports date strings (e.g. '12/31/2015') and symbolic values (e.g. 'ME-1')
Revisions:
  01/05/16 - CB - created
  01/27/16 - CB - added ending_on parameter; refactored code to support ending_on parameter
  01/28/16 - CB - refactored to consolidate parameters
*/

WITH

Timespan AS (

  SELECT  to_char(PERIOD_START,'MM/DD/YY') || ' - ' || to_char(PERIOD_END, 'MM/DD/YY') TIMESPAN
           ,PERIOD_START,PERIOD_END
           ,calendar_dt
           ,v.PERIODS,v.LENGTH,v.OFFSET,v.ENDING_ON
  FROM    (
    SELECT   add_months( trunc((SELECT efn_din(ending_on) FROM dual),'MONTH'), -(((level-1) * offset)+length)+1 ) PERIOD_START
              ,add_months( (SELECT efn_din(ending_on) FROM dual), -((level-1) * offset) ) + (86399/86400) PERIOD_END
              ,p.*
    FROM    (
      SELECT :periods PERIODS
              ,:length LENGTH
              ,:offset OFFSET
              ,:ending_on ENDING_ON
      FROM    dual
    ) p
    CONNECT BY LEVEL <= PERIODS
  ) v

)

SELECT * FROM timespan