SQL Join - MySQL/PostgreSQL difference?

Greetings.

I'm working with a product provided by a third part that interfaces to
data housed in a database of your choice.  Previously, my choice was
MySQL - apparently it handled certain queries too slowly, so I'm giving
PostgreSQL a shot.  Here's the query:

SELECT
  a.Number,
  a.Code,
  a.Text
FROM
  b,
  a
WHERE
  (b.Id = a.Id) AND
  (VersionId = 'key1') AND
  (Category = 'key2') AND
  (b.d_Id = 'key3')
ORDER BY
  a.Number;

(my apologies: I had to 'mangle' the table/column names because of NDA)

So my question is this: would this query operate differently in MySQL
than in PostgreSQL?  The reason I ask is that this query in MySQL
returns results, yet in PostgreSQL it does not.  I read a post about
PostgreSQL not supporting outer joins, but I don't have enough
experience with SQL to determine if this is such a query or not.  Please

advise.

Any help will be (as always) sincerely appreciated.

--
Brice Ruth
WebProjkt, Inc.
VP, Director of Internet Technology
http://www.webprojkt.com/