Thread

Counting bool flags in a complex query

Michael Richards <miker@scifair.acadiau.ca> — 1999-07-13T23:25:09Z

Hi.

I think I've created a monster...

Working on an email system I have the following:
Table    = usermail
+----------------------------------+--------------------------+-------+
|              Field               |              Type        | Length|
+----------------------------------+--------------------------+-------+
| contentlength                    | int4                     |     4 |
| folder                           | int4                     |     4 |
| flagnew                          | bool                     |     1 |
etc...

And:
Table    = folders
+----------------------------------+--------------------------+-------+
|              Field               |              Type        | Length|
+----------------------------------+--------------------------+-------+
| loginid                          | varchar() not null       |    16 |
| folderid                         | int4 not null default (  |     4 |
| foldername                       | varchar()                |    25 |
etc...

So each email message has an entry in usermail, and each mail folder has
an entry in folders. I need to extract the following info:
foldername, number of messages in that folder, number of messages in that
folder with flagread set, total size of all the messages in each folder

Since postgres does not appear to support outer joins, I've come up with a
really icky query that almost does what I want:

SELECT folderid,foldername,count(*),sum(contentlength) 
  FROM usermail,folders 
  WHERE usermail.loginid='michael' AND
        folders.loginid=usermail.loginid AND 
        usermail.folder=folders.folderid
  GROUP BY folderid,foldername 
UNION SELECT folderid,foldername,null,null
  FROM folders 
  WHERE loginid='michael' AND 
        folderid NOT IN 
          (SELECT folder FROM usermail WHERE loginid='michael');

WHEW!

folderid|foldername      |count|    sum
--------+----------------+-----+-------
      -4|Deleted Messages|  110| 245627
      -3|Saved Drafts    |     |       
      -2|Sent Mail       |    7|  10878
      -1|New Mail Folder |   73|8831226
       1|OOL             |    7|   8470
etc...

My final problem is to count all the messages with flagnew set to true.
The only way I can think to do this is to convert the bool value to a 1 or
0 (which I think should be a standard conversion anyway) and run a sum()
on them.

Unless anyone can come up with a better way to do this, What is the best
way to implement a conversion from bool to int?

-Michael