[vox-tech] A complicated SQL question

[Troy Arnold]

On Thu, Nov 09, 2006 at 12:49:25PM -0800, Richard S. Crawford wrote:
> I have a number of rows in my database which look something like this:
> 
> 
> id | username | canonicalname | password
> ---+----------+---------------+-----------------------
> 01 | asmith   | ART SMITH     | md5 encrypted password
> 02 | asmith1  | ART SMITH     | <NULL>
> 03 | bjones   | BILL JONES    | md5 encrypted password
> 04 | bjones12 | BILL JONES    | <NULL>
> ---+----------+---------------+-----------------------
> 
> 
> There are something like 275 entries like these.  I'm having a hell of a time 
> finding a way to select rows like 02 and 04, where canonicalname is a 
> duplicate of the same value in another row and the password is blank, and 
> then deleting those rows.  After executing my query, the table should look 
> like this:
> 
> 
> id | username | canonicalname | password
> ---+----------+---------------+-----------------------
> 01 | asmith   | ART SMITH     | md5 encrypted password
> 03 | bjones   | BILL JONES    | md5 encrypted password
> ---+----------+---------------+-----------------------
> 
> 
> Is there a simple way to execute a single select query which would pull up all 
> the rows I need?

Joining the table to itself should work.

select pw.*, pw2.cname from pw inner join pw as pw2 on pw.cname=pw2.cname
where pw.password is null and pw2.password is not null group by pw.cname;

-t