ZEND PHP 5 Certification STUDY GUIDE

Database Programming ” 151
The recordset returned by this SELECT statement will contain all books written by the
author specified in the WHERE clause (assuming, of course, that your naming convention
is consistent). You may also list more than one parameter in a WHERE clause to
further limit or broaden the results, using a number of logical conjunctions:
SELECT * FROM book
WHERE author = ’Ray Bradbury’ OR author = ’George Orwell’;
SELECT * FROM book
WHERE author = ’Ray Bradbury’ AND publisher LIKE ’%Del Ray’;
The first example statement contains an OR clause and, thus, broadens the results
to return all books by each author, while the second statement further restricts the
results with an AND clause to all books by the author that were also published by a
specific publisher. Note, here, the use of the LIKE operator, which provides a caseinsensitive
match and allows the use of the % wild character to indicate an arbitrary
number of characters. Thus, the expression AND publisher LIKE ’%Del Ray’
will match any publisher that ends in the string del ray, regardless of case.
SQL Joins
As the name implies, joins combine data from multiple tables to create a single
recordset. Many applications use extremely complex joins to return recordsets of
data spanning across many different tables. Some of these joins use subqueries
that contain even more joins nested within them. Since joins often comprise very
complex queries, they are regarded as an advanced SQL concept and many inexperienced
developers try to avoid them—for better or worse. However, they are not quite
as complicated as they are made out to be.
There are two basic types of joins: inner joins and outer joins. In both cases, joins
create a link between two tables based on a common set of columns (keys). An inner
join returns rows from both tables only if keys from both tables can be found that
satisfies the join conditions. For example:
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SELECT *
FROM book INNER JOIN book_chapter
ON book.isbn = book_chapter.isbn;