active record class in codeigniter (Delete)

<?php
/**************** Deleting Data From Database ****************/
//Generates a delete SQL string and runs the query.
$this -> db -> delete('tablename', array('id' => $id)); 
//The first parameter is the table name, 
//the second is the where clause. 
//You can also use the where() or or_where() functions instead of passing the data 
//to the second parameter of the function:


$this -> db -> where('id', $id);
$this -> db -> delete('tablename'); 


//An array of table names can be passed into delete() 
//if you would like to delete data from more than 1 table.


$tables = array('table1', 'table2', 'table3');
$this -> db -> where('id', '5');
$this -> db -> delete($tables);


//If One wants to delete all data from a table, 
//Then One can use the truncate() function, or empty_table().


$this -> db -> empty_table();


//Generates a delete SQL string and runs the query.
$this -> db -> empty_table('tablename'); 


//Generates a truncate SQL string and runs the query.


$this -> db -> from('tablename'); 
$this -> db -> truncate(); 
// OR
$this -> db -> truncate('tablename'); 






/************* Method Chaining **************************/
//Method chaining allows one to simplify syntax by connecting multiple functions


$this -> db -> select('title') -> from('mytable') -> where('id', $id) -> limit(10, 20);
$query = $this -> db -> get();






/*************** Active Record Caching **********************/
//While not "true" caching, Active Record enables you to save (or "cache") 
//certain parts of your queries for reuse at a later point in your script's execution. 
//Normally, when an Active Record call is completed, all stored information is 
//reset for the next call. 
//With caching, you can prevent this reset, and reuse information easily.


// Cached calls are cumulative. 
// If you make 2 cached select() calls, 
// And then 2 uncached select() calls, 
// This will result in 4 select() calls. 
//There are three Caching functions available:


//This function must be called to begin caching. 
//All Active Record queries of the correct type
$this -> db -> start_cache();


//This function can be called to stop caching
$this -> db -> stop_cache();


//This function deletes all items from the Active Record cache.
$this -> db -> flush_cache();




//Generates: SELECT `field1` FROM (`tablename`)
$this -> db -> start_cache();
$this -> db -> select('field1');
$this -> db -> stop_cache();
$this -> db -> get('tablename');


//Generates: SELECT `field1`, `field2` FROM (`tablename`)
$this -> db -> select('field2');
$this -> db -> get('tablename');


//Generates: SELECT `field2` FROM (`tablename`)
$this -> db -> flush_cache();
$this -> db -> select('field2');
$this -> db -> get('tablename');


//Note: The following statements can be cached: select, 
//from, join, where, like, group_by, having, order_by, set


?>