OPNQRYF (Open Query File) is the most powerful, most complex, and least documented command in the CL language. You can use it to sort and summarize data, but it can also do much more for you. It allows you to create new fields and assign values to them, perform complex joins of multiple files, create new files with existing and calculated fields, select records (even based on summarized data), and much more! The more you learn about OPNQRYF, the more opportunities you will find to use it in your applications. This book explains the ins and outs of OPNQRYF from the basic operations through the most complex mapping and selection parameters. This new edition of the best-selling book includes invaluable new material. There are new chapters on date data type, ILE, and the Year 2000 issue. The book is reorganized to make it more useful not only as a learning tool, but also as a reference for on-going value.