How to set a Postgresql default value datestamp like 'YYYYMM'?

Question

As title, how can I set a table\'s column to have the default value the current year and month, in format \'YYYYMM\', like 200905 for today?

Answer 1

Thanks for everyone who answered, and thanks for those who gave me the function-format idea, i'll really study it for future using.

But for this explicit case, the 'special yyyymm field' is not to be considered as a date field, but just as a tag, o whatever would be used for matching the exactly year-month researched value; there is already another date field, with the full timestamp, but if i need all the rows of january 2008, i think that is faster a select like

SELECT  [columns] FROM table WHERE yearmonth = '200801'

instead of

SELECT  [columns] FROM table WHERE date BETWEEN DATE('2008-01-01') AND DATE('2008-01-31')