The SAS support website
http://support.sas.com/ provides SAS-hosted support technical documents, including product documentation. There is a SAS DOC guide on the SAS SQL PROCEDURE. Also, there are supplemental technical and conference papers at the support website on the topic.
Scott Barry
SBBWorks, Inc.
SAS 9.2 SQL Procedure User's Guide
http://support.sas.com/documentation/cdl/en/sqlproc/62086/HTML/default/a002536894.htm
An Introduction to SAS PROC SQL
Timothy J Harrington, Venturi Partners Consulting, Waukegan, Illinois
http://www2.sas.com/proceedings/sugi27/p070-27.pdf