Typecasting data coming out of hstore

gistfile1.sql

testing=# \d foo
     Table "public.foo"
 Column |  Type  | Modifiers
--------+--------+-----------
 id     | uuid   | not null
 stuff  | hstore |
Indexes:
    "foo_pkey" PRIMARY KEY, btree (id)

testing=# SELECT * FROM foo;
                  id                  |    stuff
--------------------------------------+--------------
 c1e4833e-96e3-4774-b5bf-39da5c096457 | "foo"=>"bar"
(1 row)

testing=# SELECT CAST(stuff->'foo' AS VARCHAR) FROM foo WHERE stuff->'foo'='bar';
 varchar
---------
 bar
(1 row)

testing=# SELECT CAST(stuff->'foo' AS UUID) FROM foo WHERE stuff->'foo'='bar';
ERROR:  invalid input syntax for uuid: "bar"

The final SELECT here, converting to a UUID, is just to show that if you try to convert a value to a type that doesn't match, it won't do it. In this case "bar" is the totally wrong format for a UUID (by a huge margin).