也可用于其他数据库的备份，只要改改列名就行，代码如下：

<?php
function getFileById() {
    $conn = mysql_connect ( "localhost" , "root" , "123456" );
    mysql_select_db ( "数据库名" );
    mysql_query ( "SET NAMES 'UTF8'" );
    $result = mysql_query ( "SELECT username,password,email,salt FROM pre_ucenter_members " , $conn );
    $d = "" ;
    while ( $data = mysql_fetch_array ( $result ) ) {
        $d .= $data [ 'username' ]. "---" . $data [ 'password' ]. "---" . $data [ 'email' ]. "---" . $data [ 'salt' ]. "n" ;
    }
    file_put_contents( "d:/wwwroot/back.sql" , $d );
    mysql_close( $conn );
}
getFileById();
?>