difficult query

Hi,

I'd like to ask how to write sql query returning following results without
using any other table than table1 (e.g. without outer join with table
containing all possible day numbers...)

table1:
day  |  data
------------
1    |  x
1    |  x
2    |  x
4    |  x
4    |  x


I'd like to write query returning this:

query results:
day | number of records for a day
----------------------
1   |  2
2   |  1
3   |  0   <--- !!!
4   |  2

Is it possible to do this in sql?

thanks a lot,          kuba