Re: Newbie question

[Nick Roper]

Michael,

First of all, what you're looking at here isn't MySQL syntax - it's PHP, which is a programming language that is widely used to expose information in a MySQL database via a web-browser.

Anyway, to answer your questions:

mysql_result() is a PHP function that can be used to fetch data from a specific field(column) in a recordset. It takes three parameters which, in the context of your example, are as follows:

$sql - the result set returned by mysql_query()
$x - a pointer to a row number in the recordset
"subcategories" - the field/column name from which to get the data on that row

So, in this example, a for loop is being used to retrieve data from the "subcategories" field for rows 0 to $n_subcategories (which presumably is being assigned elsewhere?) of the recordset.

As for the LEFT JOIN, the join is actually on a table named (something)categories.

The syntax '... {$prefix}categories AS {$prefix}subcategories ..." does the following:

Suppose that the $variable contained 'foo', this would be substituted into the string as follows:

'... foocategories AS foosubcategories ..."

'foosubcategories' then becomes an alias for the real table name, and can be used elsewhere.

Variable sunstitution in PHP works within "" "" quoted string, so "my name is $name" will return (say) "my name is Nick" if $name is 'Nick'. However, a problem occurs if you try to prepend or append a variable name to a literal string, for example, if you had 'Sun' stored in a variable called $shortname, and then tried to display the full day name with: "Today is $shortnameday " (to get 'Sunday'), PHP would actually see the variable name as '$shortdayname' - which doesn't exist. To get round this { } brackets are used to isolate the variable name and force a substitution, i.e: "Today is {$shortname}day "


Hope this hepls,

Nick


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Nick Roper