PL/SQL Help Pages
Using PL/SQL	Oracle PL/SQL User’s Guide and Reference	/opt/oracle8/product/8.1.5/plsql/demo

PL/SQL is an extension to SQL. PL/SQL is a transaction processing language that supports procedural constructs, variable declarations, and robust error handling. Within the same PL/SQL block, you can use SQL and all the PL/SQL extensions. The main advantage of embedded PL/SQL is better performance. Unlike SQL, PL/SQL allows you to group SQL statements logically and send them to Oracle in a block rather than one by one. This reduces network traffic and processing overhead.