Delete enregistrements > aux x derniers .

<?
include "sqlconnect.php";
function imp($char,$tag){
	foreach($char as $key=>$value){
	$char[$key] = $value;
	}
	$char = implode($tag,$char);
	return $char;
}
	$sql = "SELECT date_timestamp FROM xxxx ORDER BY date_timestamp DESC LIMIT 0,70";
	$query = mysql_query($sql);
	while($row = mysql_fetch_array($query)){
	$date[] = $row[date_timestamp];
	}
mysql_query("DELETE FROM xxxx WHERE date_timestamp NOT IN (".implode(',', $date).")");
?> 

<?php
require_once('sqlconnect.php');

$query = 'SELECT id FROM xxxx ORDER BY date_timestamp DESC LIMIT 0,70';
$query_result = mysql_query($query);

//Récupération des id des 70 derniers enregistrements
while($row = mysql_fetch_array($query)):
	$id_array[] = $row['id'];
endwhile;


foreach($id_array as $key=>$value):
	mysql_query('DELETE FROM xxxx WHERE id = '.$value.' LIMIT 1');
endforeach;


?> 

<?php 
require_once('sqlconnect.php'); 

$query = 'SELECT id FROM xxxx ORDER BY date_timestamp DESC LIMIT 0,70'; 
$query_result = mysql_query($query); 

//Récupération des id des 70 derniers enregistrements 
while($row = mysql_fetch_array($query_result)): 
    $id_array[] = $row['id']; 
endwhile; 

//Suppression pour chaque id récupéré auparavant 
foreach($id_array as $key=>$value): 
    mysql_query('DELETE FROM xxxx WHERE id = '.$value.' LIMIT 1'); 
endforeach; 


?>