This manual is part of the official reference documentation for PostgreSQL 9.0. It documents the client and server interfaces to PostgreSQL: the C/C++ interface libpq, the embedded SQL/C compiler ECPG and the server-side languages PL/pgSQL, PL/Tcl, PL/Perl and PL/Python. Each chapter includes reference documentation and examples. In particular, the use of triggers, rules and views is described in detail. The PL/pgSQL chapter also includes a guide to porting Oracle PL/SQL functions to PostgreSQL. The other volumes of this series are Volume 1A "The SQL Language" (ISBN 978-1-906966-04-1), Volume 1B, the "SQL Command Reference" (ISBN 978-1-906966-05-8), and Volume 3, the "Server Administration Guide" (ISBN 978-1-906966-07-2). For each copy of this manual sold 1 USD is donated to the PostgreSQL project by the publisher, Network Theory Ltd.