MySQL and the WHERE part

In the previous chapter, we saw how we could use the SELECT query to get data from the database, but we weren't exactly very picky about which data to get. As you will realize in the following chapters, the SELECT statement is very powerful and allows you to do pick, prioritize and sort your data in all sorts of way before returning it. In this chapter we will have a look at the WHERE part, which allows you to decide which data to select.

An SQL statement with a WHERE part could look like this:

SELECT id, name, country FROM test_users WHERE id > 3

You can of course set more than one criteria:

SELECT id, name, country FROM test_users WHERE id > 3 AND id < 8

And you can use strings as criteria as well:

SELECT id, name, country FROM test_users WHERE country = 'USA'

You can even use MySQL's own functions in the WHERE part. For instance like this, where we use the SUBSTRING() function in MySQL to get all users starting with the letter "S":

SELECT id, name, country FROM test_users WHERE SUBSTRING(name, 1, 1) = 'S'

To test the examples above, you can use this test code we wrote in a previous chapter. Simply put one of the queries inside the mysql_query() function and run the code:

mysql_connect("localhost", "username", "password");
mysql_select_db("my_database");

$query = mysql_query("Insert your SQL query here");
while($row = mysql_fetch_array($query))
    echo $row["name"] . " is from " . $row["country"] . "<br />";

Table Of Contents

• About PHP

Requirements

• Introduction
• Webserver
• PHP
• Using it

The editor

• Introduction
• Previewing
• Syntax checking
• Debugging

Basic PHP

• Hello world
• PHP tags
• Variables
• If statements
• More if statements
• The switch statement
• Loops
• Including files
• Functions

Data types

• Introduction
• Working with numbers
• Working with strings
• More strings
• Working with arrays
• More arrays

Classes

• Introduction
• Defining and using a class
• Constructors and destructors
• Visibility
• Inheritance
• Abstract classes
• Static classes
• Class constants
• The "final" keyword

PHP and MySQL

• Introduction
• Connecting to MySQL
• Retrieving data
• The WHERE part
• The ORDER BY part
• The LIMIT part
• Handling errors

State

• Cookies

Working with forms

• GET and POST
• Validating form input