Finding distinct months using find_by_sql

I’m wondering if someone might be able to offer me a solution to the
following problem that has so far stumped me.
I’m trying to get the distinct months (and years) from a date field to
display as a list in a view. For example, there might be a number of
records stored with dates in the table ‘headlines’:
name date
record1 21-09-2008
record2 15-09-2008
record3 03-08-2008
record4 02-08-2008
record5 12-07-2008

From which I’d like to get all distinct years and months to display in
a view something like what might be seen under the ‘Archives’ section
of a blog page, like this:
September 2008
August 2008
July 2008

I have tried to set the following sql statement in my controller to
find the months using find_by_sql:
@headlines_month = Headline.find_by_sql(“SELECT distinct
MONTHNAME(date) FROM headlines”)

However, this errors out as:

PGError: ERROR: function monthname(date) does not exist at character
HINT: No function matches the given name and argument types. You may
need to add explicit type casts.
: SELECT distinct MONTHNAME(date) FROM headlines

It’s monthname() which is what’s causing it to error out as, if i
remove monthname() there are no problems.
I’m not sure if this is a problem of my limited understanding of that
rails command or an error with my sql statement but I’m out of ideas
so if anyone might have an idea for an effective solution - or can
point me in the right direction - I’d very much appreciate it.

Thanks in advance.


it looks like your Postgresql doesn’t support the function monthname().
Try this statement on a Postgresql-console.
Which Version of Postgresql do you have installed?


Am Dienstag, den 23.09.2008, 10:43 -0700 schrieb it:

Thanks for the reply Johannes. I think you’re right about Postgresql
not supporting monthname().

I managed to get round this using the following:
@headlines_month = Headline.find_by_sql(“SELECT DISTINCT
DATE_PART(‘year’, date) as year, DATE_PART(‘month’, date) as month
FROM headlines ORDER BY year DESC”)

I appreciate your taking time to reply.
Best regards

To display the month name you could either:

  1. Create a function that would return the month name based on the
    month numeric value and call it from your SQL statement. This would
    allow you to use the same functionality in more than 1 statement,
  2. Use a case clause. Not sure how the syntax would be in Postgresql.
    Something like this:
    case when DATE_PART(‘month’, date) = 1 then ‘January’
    when DATE_PART(‘month’, date) = 2 then ‘February’