PostgreSQL equivelant of this MySQL query

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@domain.com' this should return
'domain.com/person'.

   Thanks for the help!

Madison