9.4.2 Querying and formatting: mysql_query() and mysql_num_rows()This is NOT the latest copy of this book; click here for the latest version.
resource mysql_query ( string query [, resource link_identifier])
int mysql_num_rows ( [resource result])
The majority of your interaction with MySQL in PHP will be done using the mysql_query() function, which takes one parameter - the SQL query you want to perform. It will then perform that query and return a special resource known as a MySQL result index - this resource contains all the rows that matched your query.
This result index resource is the return value of mysql_query(), and you should save it in a variable for later use - whenever you want to extract rows from the results, count the number of rows, etc, you need to use this value.
One other key function is mysql_num_rows(), which takes a MySQL result index as its parameter, and returns the number of rows inside that result - this is the number of rows that matched the query you sent in mysql_query(). With the two together we can write our first database enabled script:
<?php
mysql_connect("localhost", "phpuser", "alm65z");
mysql_select_db("phpdb");
$result = mysql_query("SELECT * FROM usertable");
$numrows = mysql_num_rows($result);
print "There are $numrows people in usertable\n";
?>
As you can see, we capture the return value of mysql_query() inside $result, then use on the very next line - this MySQL result index is used quite heavily, so it is important to keep track of it. The exception to this is when you are executing a write query in MySQL - you might not want to know the result.
One helpful feature of mysql_query() is that it will return false if the query is syntactically invalid - that is, if you have used a bad query. This means that very often it is helpful to check the return value even if you are writing data - if the data was not written successfully, mysql_query() will tell you so with the return value.
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