HP 3000 Manuals HP 3000 Manuals
Coding Considerations
A static application is one that is preprocessed in full preprocessing
mode (defined further in the ALLBASE/SQL application programming guides)
and contains at least one static SQL statement. This means that a module
is generated at preprocessing time, and this module must be installed in
any DBEnvironment in which the application is running.
An application containing only dynamic SQL statements is termed a dynamic
application. Such an application does not require a module. It can be
preprocessed in either full preprocessing mode or in static conversion
mode.
Suppose you are coding a user interface to the PurchDB.Parts database.
While there is only one way of creating a static application, there are
two ways of creating a dynamic application. They are as follows:
1. At coding time, by embedding only dynamic statements (as defined
in the previous section), you are assured of a dynamic
application. Such an application can be preprocessed in either
full preprocessing mode or static conversion mode. With static
conversion mode, a DBEnvironment name need not be specified on the
command line.
2. At preprocessing time, by choosing static conversion mode, your
resulting application is dynamic. If your source code contains
static statements, they are converted to dynamic ones. Any
dynamic statements are unchanged and remain dynamic.
Coding an Application that can be Either Static or Dynamic
Suppose you are coding a user interface to the PurchDB.Parts database.
You know at coding time that you want the user to have the option of
selecting information from each table in the database environment. You
also know the exact format of each select statement. In addition, you
want the user to be able to enter an ad hoc query, one that meets their
particular needs at run time, for any of the tables in the database. The
displayed menu might look something like the following:
Menu to Select Parts Information
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1. PARTS 3. ORDERS 5. VENDORS 7. REPORTS
2. INVENTORY 4. ORDER ITEMS 6. SUPPLY PRICE 8. AD HOC QUERY
You could code seven static SELECT statements and a dynamic select
statement (for the ad hoc query). Depending on your requirements, you
could preprocess this application in full preprocessing mode or static
conversion mode. Full preprocessing could enhance performance when users
most often choose one of the static SELECT statements. Static conversion
processing would result in a portable application, ideal for use in a
distributed database environment.
Converting a Static Application to a Dynamic Application
There are two ways of converting a static application to a dynamic
application. One method is to change the source code to contain the
required dynamic SQL statements. (The ALLBASE/SQL application
programming guides provide complete information about coding with dynamic
SQL statements.) The second method is to preprocess the application
using static conversion mode. The following paragraphs discuss use of
the second method with an application originally designed to use full
preprocessing mode.
By choosing the DYNAMIC option at preprocessing time, you avoid having to
make major changes to your existing source code. You also maintain the
flexibility of preprocessing the source code to be either static or
dynamic simply by changing the preprocessor command line options.
Unlike other preprocessing modes in which any DECLARE CURSOR statements
are commented out, static preprocessing mode converts DECLARE CURSOR
statements to executable code. Therefore, if your existing code contains
such a statement in a non-executable portion of the code, you must move
the statement to an executable portion of the application. In the C
language, for example, you would declare the cursor within curly brackets
following any data declaration statements within a given block. For
Pascal, position the statement within a BEGIN/END block.
Another consideration is that host variables used in static statements
(except for BULK FETCH and BULK SELECT statements) must adhere to the
restrictions for dynamic parameters. See the chapter in this document
titled "Using Parameter Substitution in Dynamic Statements" for further
details.
Enhancing Performance
By default, ALLBASE/SQL does authorization checks on a dynamic query each
time it is executed. By setting the authorize once per session flag to
ON, you insure that authorization checks on dynamic queries are performed
only the first time the query is executed during a given user session.
You can set this flag by means of the SQLUtil ALTDBE command described in
the ALLBASE/SQL Database Administration Guide.