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9.1 PL/SQL
The Procedure Language
extension to SQL (PL/SQL)
is Oracle's proprietary programming language. It is
used both server-side and client-side:On the server side
PL/SQL is used in the Oracle database to program stored procedures
and triggers.
On the client side
PL/SQL is used in Oracle's declarative development
tools, Oracle Forms and Oracle Reports, to program behavior.
PL/SQL's strengths lie in its seamless integration
with SQL and in its excellent server-side performance. Because
Oracle's tools, Oracle Forms and Oracle Reports,
also use PL/SQL as their programming language, these tools can
leverage both seamless integration with the database and existing
PL/SQL database programmer expertise for client-side development.
9.1.1 Using PL/SQL
PL/SQL uses the same datatypes as SQL in the database; hence, no
datatype conversions are necessary. PL/SQL effectively adds
procedural language constructs, such as IF-THEN-ELSE logic, FOR
loops, and so on, to SQL. Because PL/SQL stored procedures are
executed in the database, this capability eliminates the data access
delays caused by moving data across a network. This makes PL/SQL the
superior choice for data-intensive manipulations in the database.Oracle Application Server provides a way to produce dynamic content
via Oracle database stored procedures. The execution of stored
procedures for web applications is facilitated through the Oracle
HTTP Server module mod_plsql; the Oracle HTTP
Server was described in detail in Chapter 5.PL/SQL is a rich and powerful language that we only touch upon in
this book. For much more detailed information, see Oracle
PL/SQL Programming (O'Reilly).
9.1.2 PL/SQL Web Applications
Oracle HTTP Server
uses the
mod_plsql
module to route stored procedure requests to an Oracle database.
mod_plsql provides a CGI environment for stored
procedures. A request URI routed to mod_plsql from
the Oracle HTTP Server is mapped to a corresponding stored procedure
in the database as follows:The name of the stored
procedureschema, package name, and procedure name (as required
to eliminate ambiguity)is specified in the URI.Any HTTP parameter values are mapped to stored procedure parameters
with exactly the same names as the HTTP parameters.Extra path information, cookies, and CGI environment variables are
also made available.
The logic of a stored procedure can use any of this information to
formulate a response in the form of text that is then streamed back
to the requester through mod_plsql to the Oracle
HTTP Server, and so on. Two software development kits are available
to aid the developer: the PL/SQL Web Toolkit and PL/SQL Server Pages.
If you're familiar with Java, note that these can be
compared to Java servlets and JSPs, respectively.PL/SQL Web Toolkit
This toolkit provides a set of Oracle stored
procedure packages (e.g., HTP,
HTF, OWA_UTIL) that allow a
PL/SQL programmer to call procedures or functions to produce HTML
output. These packages also provide access to CGI environment
variables and cookies. Using the PL/SQL Web Toolkit, a programmer
writes a stored procedure that outputs HTML tags and data.
PL/SQL Server Pages
In contrast, PL/SQL Server Pages are HTML files with
embedded PL/SQL scriptlets. The scriptlets
(small pieces of PL/SQL code) may call PL/SQL Web Toolkit procedures
and functions. PSPs are compiled into stored procedures when they are
loaded into the database using the loadpsp
utility.
The difference between using the PL/SQL Web Toolkit and using PL/SQL
Server Pages is that PL/SQL Web Toolkit procedures are PL/SQL
programs with embedded
HTML, while PL/SQL Server Pages are
HTML files with embedded PL/SQL. The PL/SQL Web Toolkit is typically
a more appropriate choice for programmers, whereas PSPs are a better
fit for web designers. Ultimately, every PSP becomes a stored
procedure.
