http://www.php-mysql-tutorial.com/wikis/mysql-tutorials/using-php-to-backup-
mysql-databases.aspx

要么

$tableName  = 'mypet';
$backupFile = 'backup/mypet.sql';
$query      = "SELECT * INTO OUTFILE '$backupFile' FROM $tableName";
$result = mysql_query($query);

要么

$backupFile = $dbname . date("Y-m-d-H-i-s") . '.gz';
$command = "mysqldump --opt -h $dbhost -u $dbuser -p $dbpass $dbname | gzip >     $backupFile";
system($command);