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222 Understanding Web Applications
Accessing a database
An application server lets you work with server-side resources such as
databases. For example, a dynamic page may instruct the application server
to extract data from a database and insert it into the page’s HTML. For
more information, see
Appendix A, “Beginner’s Guide to Databases” in
Using Dreamweaver .
The instruction to extract data from a database is called a database query. A
query consists of search criteria expressed in a database language called
SQL (Structured Query Language). The SQL query is written into the
page’s server-side scripts or tags.
An application server cannot communicate directly with a database because
the database’s proprietary format renders the data undecipherable in much
the same way that a Microsoft Word document opened in Notepad or
BBEdit may be undecipherable. The application server can communicate
with the database only through the intermediary of a database driver:
software that acts like an interpreter between the application server and the
database.
After the driver establishes communication, the query is executed against
the database and a recordset is created. A recordset is a set of data extracted
from one or more tables in a database. The recordset is returned to the
application server, which uses the data to complete the page.
Here’s a simple database query written in SQL:
SELECT lastname, firstname, fitpoints
FROM employees
This statement creates a three-column recordset and fills it with rows
containing the last name, first name, and fitness points of all employees in
the database. For more information, see
Appendix B, “SQL Primer” in
Using Dreamweaver .