Date And Time Functions
SQLite supports five date and time functions as follows:
1. date(timestring, modifier, modifier, ...)
...
The time string can be followed by zero or more modifiers that alter the date and time string. The available modifiers are as follows.
...
7. start of month
...
Example
Compute the last day of the current month.
SELECT date('now','start of month','+1 month','-1 day');
(c)
http://www.sqlite.org/lang_datefunc.html 
