www.orafaq.com/wiki/SQL_FAQ
Using PL/SQL Collections and Records
download.oracle.com/docs/cd/B19306_01/appdev.102/b14261/collections.htm#i20446
Datatype Comparison Rules
download.oracle.com/docs/cd/B19306_01/server.102/b14200/sql_elements002.htm#i46862
Some stuff in Russian language:
www.firststeps.ru/sql/oracle/oracle1.html