When we're creating some kind of CMS is customary to classify content into categories, where they can have children, grandchildren, great-etc.

For example: Our table category has an id, name, father's, where the latter is the id of another category.

Therefore we can complicate print that list correctly. To resolve this we can make a small function:

 sacarHijos function ($ id_padre, $ level)
 (
     $ Result = mysql_query ("SELECT id, name, parent FROM categories WHERE parent = $ id_padre");

     if (mysql_num_rows ($ result))
     (
	 $ Level = $ level .'-----';
	 while ($ d = mysql_fetch_row ($ result))
	 (
	     / / Print tree categories
	     echo $ level. '>'. $ d [1];

	     / / Call the function again to print other children
	     sacarHijos ($ d [0], $ level);
	 )
     )
 )

Of course when you call the function sacarHijos the value that is passed in the variable $ level may be empty, eg

 / / We tell the function to print the daughters of the father 00 categories, namely the root.
 sacarHijos (00 ,'');

This allows us to print a tree or hierarchy of categories to print in tables, list of menu options, etc.