SQL

Carnegie Mellon University, Pittsburgh, Pennsylvania: SQL Reference and Resources Guide
Check Carnegie Mellon University for information on SQL, including information, programming resources, software, tools, DBMS information, and much more.

Inquiry.com: Ask The SQL Pro
Browse Inquiry.com for a Q and A section focusing on SQL Arithmetics, Introduction to SQL, SQL Server Security, Syntax and more.

PostgreSQL.org
Check PostgreSQL.org for information on Object-Relational DBMS to support almost all SQL constructs, transactions, and user-defined types and functions.

University of California, Berkeley: SQL FAQs
Check University of California, Berkeley for introductory information, query performance, and problem-solving for SQL programming language.