PostgreSQL equivelant of this MySQL query

[Madison Kelly <linux@xxxxxxxxxxx>]

Hi all,

  I am reading through some docs on switching to Postfix with a SQL 
backend. The docs use MySQL but I want to use PgSQL so I am trying to 
adapt as I go. I am stuck though; can anyone help give me the PgSQL 
equiv. of:

SELECT 
CONCAT(SUBSTRING_INDEX(usr_email,'@',-1),'/',SUBSTRING_INDEX(usr_email,'@',1),'/') 
FROM users WHERE usr_id=1;

  If the 'usr_email' value is 'person@xxxxxxxxxx' this should return 
'domain.com/person'.

  Thanks for the help!

Madison