mysql分页pagination

http://www.phpjabbers.com/php--mysql-select-data-and-split-on-pages-php25.html

returns 20 records sorted by name starting from the first record:

$sql = "SELECT * FROM students ORDER BY name ASC LIMIT 0, 20";

this next query shows 20 records sorted again by name but this time it will start from the 50th record. 

$sql = "SELECT * FROM students ORDER BY name ASC LIMIT 50, 20";