Postgres: select the sum of values and then sum this again

Question

I tried a lot but can´t find the right way. If I select values in Postgres and sum them it looks like this:

SELECT name,sum(size) as total
FROM mytable group by name order by name;

How can I alter this so it also sum all values in total? I think I need a subselect but how?

Answer 1

Try this:

SELECT sum(a.total)
FROM (SELECT sum(size) as total
      FROM mytable group by name) a

UPDATE I'm sorry, I don't read that you want it all in the same query. For this reason the answer of greg it's better. However, other possibility if you have a postgresql version >= 9:

WITH mytableWith (name, sum) as
     (SELECT name, sum(size)
      FROM mytable
      GROUP BY name)
SELECT 'grand total' AS name, 
       sum(sum) AS sum
FROM mytableWith
UNION ALL
SELECT name, sum
FROM mytableWith