ZEND PHP 5 Certification STUDY GUIDE

150 ” Database Programming
DELETE FROM book WHERE isbn = ’0812550706’;
i
Retrieving Data
As we mentioned earlier, relational database are biased toward read operations;
therefore, it follows that the most common SQL statement is designed to extract data
from a database.
To retrieve data from any SQL database engine, you must use a SELECT statement;
SELECT statements range from very simple to incredibly complex, depending on your
needs. Its most basic form, however, is simple and easy to use:
SELECT * FROM book;
The statement begins with the verb or action keyword SELECT, followed by a commaseparated
list of columns to include in the dataset retrieved. In this case, we use the
special identifier * , which is equivalent to extracting all of the columns available in
the dataset. Following the list of columns is the keyword FROM, which is itself followed
by a comma-separated list of tables. This statement retrieves data from only one
table, the book table.
The format in which the dataset is returned to PHP by the database system depends
largely on the system itself and on the extension you are using to access it; for example,
the “traditional” MySQL library returns datasets as resources from which you can
extract individual rows in the form of arrays. Newer libraries, on the other hand, tend
to encapsulate result sets in objects.
You will rarely need to gain access to all of the records in a table—after all, relational
databases are all about organizing data and making it easily searchable. Therefore,
you will most often find yourself limiting the rows returned by a SELECT statement
using a WHERE clause. For example, for the book table, you may wish to retrieve
all books written by a specific author. This is possible using WHERE.
Licensed to 482634 - Amber Barrow (itsadmin@deakin.edu.au)
SELECT * FROM book WHERE author = ’Ray Bradbury’;