[PERFORM] sum of all values

[Madison Kelly]

Hi all,
  Is there a fast(er) way to get the sum of all integer values for a 
certain condition over many thousands of rows? What I am currently doing 
is this (which takes ~5-10sec.):

SELECT SUM (a.file_size) FROM file_info_1 a, file_set_1 b WHERE 
a.file_name=b.fs_name AND a.file_parent_dir=b.fs_parent_dir AND 
a.file_type=b.fs_type AND b.fs_backup='t';

  I need to keep parts of the data in two tables. I currently use 
'file_name/fs_name', 'file_parent_dir/fs_parent_dir' and 
'file_type/fs_type' to match the entries in the two tables. The 
'file_info_#' table is frequently dropped and re-created so this was the 
only way I could think to match the data.

  I am hoping that maybe there is something I can do differently that 
will return this value a lot faster (ideally within a second). I know 
that this is heavily dependant on the system underneath but the program 
is designed for Joe/Jane User so I am trying to do what I can in the 
script and within my DB calls to make this as efficient as possible. I 
realise that my goal may not be viable.

  Here are the schemas, in case they help:
tle-bu=> \d file_info_1                Table "public.file_info_1"
     Column      |  Type   |         Modifiers
-----------------+---------+----------------------------
 file_acc_time   | bigint  | not null
 file_group_name | text    | not null
 file_group_uid  | integer | not null
 file_mod_time   | bigint  | not null
 file_name       | text    | not null
 file_parent_dir | text    | not null
 file_perm       | text    | not null
 file_size       | bigint  | not null
 file_type       | text    | not null default 'f'::text
 file_user_name  | text    | not null
 file_user_uid   | integer | not null
Indexes:
    "file_info_1_display_idx" btree (file_parent_dir, file_name, file_type)
    "file_info_1_search_idx" btree (file_parent_dir, file_name, file_type)
tle-bu=> \d file_set_1               Table "public.file_set_1"
    Column     |  Type   |         Modifiers
---------------+---------+----------------------------
 fs_backup     | boolean | not null default true
 fs_display    | boolean | not null default false
 fs_name       | text    | not null
 fs_parent_dir | text    | not null
 fs_restore    | boolean | not null default false
 fs_type       | text    | not null default 'f'::text
Indexes:
    "file_set_1_sync_idx" btree (fs_parent_dir, fs_name, fs_type)
  Thanks all!
Madison
---------------------------(end of broadcast)---------------------------
TIP 9: the planner will ignore your desire to choose an index scan if your
     joining column's datatypes do not match