static virtual columns as result?

Hello,

I "have" this two tables:

Table Cat:
id|A|B
--+-+-
1|3|5
2|5|8
3|6|9

Table Pr:
id|Catid|
--+-
1|3
2|2
3|1

I need replace "Catid" column for corresponding values A and B (Table
Cat) in Table Pr.

Virtual table like this:
Table Pr:
id|Catid|A|B
--+-+-+
1|3|6|9
2|2|5|8
3|1|3|5

Something like this, but that works,...

SELECT * FROM pr WHERE pr.a /*> 1 AND*/*//*
<https://www.google.es/search?hl=es&sa=X&ei=ULbyT9uKGYSt0QWNy4CwCQ&ved=0CEUQvwUoAQ&q=between&spell=1>
pr.b < 10;

With subqueries is too slow:
SELECT * FROM "Pr" AS p, (SELECT "id" AS cid FROM "Cat" WHERE "lft" > 1
AND "rgt" < 10) AS c WHERE p."Cat"=c."cid" AND (...)) ORDER BY "Catid"
ASC OFFSET 0 LIMIT 40

Any suggestion?