我对MySQL和PHP完全陌生，我正在尝试进一步开发AndroidIM项目。 这是它基于的PHP服务器代码：
<?php
error_reporting(0);
require_once("mysql.class.php");
$dbHost = "localhost";
$dbUsername = "username";
$dbPassword = "password";
$dbName = "name";
$db = new MySQL($dbHost,$dbUsername,$dbPassword,$dbName);
// if operation is failed by unknown reason
define("FAILED", 0);
define("SUCCESSFUL", 1);
// when signing up, if username is already taken, return this error
define("SIGN_UP_USERNAME_CRASHED", 2);
// when add new friend request, if friend is not found, return this error
define("ADD_NEW_USERNAME_NOT_FOUND", 2);
// TIME_INTERVAL_FOR_USER_STATUS: if last authentication time of user is older
// than NOW - TIME_INTERVAL_FOR_USER_STATUS, then user is considered offline
define("TIME_INTERVAL_FOR_USER_STATUS", 60);
define("USER_APPROVED", 1);
define("USER_UNAPPROVED", 0);
$username = (isset($_REQUEST['username']) && count($_REQUEST['username']) > 0)
? $_REQUEST['username']
: NULL;
$password = isset($_REQUEST['password']) ? md5($_REQUEST['password']) : NULL;
$port = isset($_REQUEST['port']) ? $_REQUEST['port'] : NULL;
$action = isset($_REQUEST['action']) ? $_REQUEST['action'] : NULL;
if ($action == "testWebAPI")
{
if ($db->testconnection()){
echo SUCCESSFUL;
exit;
}else{
echo FAILED;
exit;
}
}
if ($username == NULL || $password == NULL)
{
echo FAILED;
exit;
}
$out = NULL;
error_log($action."\r\n", 3, "error.log");
switch($action)
{
case "authenticateUser":
if ($userId = authenticateUser($db, $username, $password))
{
// providerId and requestId is Id of a friend pair,
// providerId is the Id of making first friend request
// requestId is the Id of the friend approved the friend request made by providerId
// fetching friends,
// left join expression is a bit different,
// it is required to fetch the friend, not the users itself
$sql = "select u.Id, u.username, (NOW()-u.authenticationTime) as authenticateTimeDifference, u.IP,
f.providerId, f.requestId, f.status, u.port
from friends f
left join users u on
u.Id = if ( f.providerId = ".$userId.", f.requestId, f.providerId )
where (f.providerId = ".$userId." and f.status=".USER_APPROVED.") or
f.requestId = ".$userId." ";
//$sqlmessage = "SELECT * FROM `messages` WHERE `touid` = ".$userId." AND `read` = 0 LIMIT 0, 30 ";
$sqlmessage = "SELECT m.id, m.fromuid, m.touid, m.sentdt, m.read, m.readdt, m.messagetext, u.username from messages m \n"
. "left join users u on u.Id = m.fromuid WHERE `touid` = ".$userId." AND `read` = 0 LIMIT 0, 30 ";
if ($result = $db->query($sql))
{
$out .= "<data>";
$out .= "<user userKey='".$userId."' />";
while ($row = $db->fetchObject($result))
{
$status = "offline";
if (((int)$row->status) == USER_UNAPPROVED)
{
$status = "unApproved";
}
else if (((int)$row->authenticateTimeDifference) < TIME_INTERVAL_FOR_USER_STATUS)
{
$status = "online";
}
$out .= "<friend username = '".$row->username."' status='".$status."' IP='".$row->IP."' userKey = '".$row->Id."' port='".$row->port."'/>";
// to increase security, we need to change userKey periodically and pay more attention
// receiving message and sending message
}
if ($resultmessage = $db->query($sqlmessage))
{
while ($rowmessage = $db->fetchObject($resultmessage))
{
$out .= "<message from='".$rowmessage->username."' sendt='".$rowmessage->sentdt."' text='".$rowmessage->messagetext."' />";
$sqlendmsg = "UPDATE `messages` SET `read` = 1, `readdt` = '".DATE("Y-m-d H:i")."' WHERE `messages`.`id` = ".$rowmessage->id.";";
$db->query($sqlendmsg);
}
}
$out .= "</data>";
}
else
{
$out = FAILED;
}
}
else
{
// exit application if not authenticated user
$out = FAILED;
}
break;
case "signUpUser":
if (isset($_REQUEST['email']))
{
$email = $_REQUEST['email'];
$sql = "select Id from users
where username = '".$username."' limit 1";
if ($result = $db->query($sql))
{
if ($db->numRows($result) == 0)
{
$sql = "insert into users(username, password, email)
values ('".$username."', '".$password."', '".$email."') ";
error_log("$sql", 3 , "error_log");
if ($db->query($sql))
{
$out = SUCCESSFUL;
}
else {
$out = FAILED;
}
}
else
{
$out = SIGN_UP_USERNAME_CRASHED;
}
}
}
else
{
$out = FAILED;
}
break;
case "sendMessage":
if ($userId = authenticateUser($db, $username, $password))
{
if (isset($_REQUEST['to']))
{
$tousername = $_REQUEST['to'];
$message = $_REQUEST['message'];
$sqlto = "select Id from users where username = '".$tousername."' limit 1";
if ($resultto = $db->query($sqlto))
{
while ($rowto = $db->fetchObject($resultto))
{
$uto = $rowto->Id;
}
$sql22 = "INSERT INTO `messages` (`fromuid`, `touid`, `sentdt`, `messagetext`) VALUES ('".$userId."', '".$uto."', '".DATE("Y-m-d H:i")."', '".$message."');";
error_log("$sql22", 3 , "error_log");
if ($db->query($sql22))
{
$out = SUCCESSFUL;
}
else {
$out = FAILED;
}
$resultto = NULL;
}
$sqlto = NULL;
}
}
else
{
$out = FAILED;
}
break;
case "addNewFriend":
$userId = authenticateUser($db, $username, $password);
if ($userId != NULL)
{
if (isset($_REQUEST['friendUserName']))
{
$friendUserName = $_REQUEST['friendUserName'];
$sql = "select Id from users
where username='".$friendUserName."'
limit 1";
if ($result = $db->query($sql))
{
if ($row = $db->fetchObject($result))
{
$requestId = $row->Id;
if ($row->Id != $userId)
{
$sql = "insert into friends(providerId, requestId, status)
values(".$userId.", ".$requestId.", ".USER_UNAPPROVED.")";
if ($db->query($sql))
{
$out = SUCCESSFUL;
}
else
{
$out = FAILED;
}
}
else
{
$out = FAILED; // user add itself as a friend
}
}
else
{
$out = FAILED;
}
}
else
{
$out = FAILED;
}
}
else
{
$out = FAILED;
}
}
else
{
$out = FAILED;
}
break;
case "responseOfFriendReqs":
$userId = authenticateUser($db, $username, $password);
if ($userId != NULL)
{
$sqlApprove = NULL;
$sqlDiscard = NULL;
if (isset($_REQUEST['approvedFriends']))
{
$friendNames = split(",", $_REQUEST['approvedFriends']);
$friendCount = count($friendNames);
$friendNamesQueryPart = NULL;
for ($i = 0; $i < $friendCount; $i++)
{
if (strlen($friendNames[$i]) > 0)
{
if ($i > 0 )
{
$friendNamesQueryPart .= ",";
}
$friendNamesQueryPart .= "'".$friendNames[$i]."'";
}
}
if ($friendNamesQueryPart != NULL)
{
$sqlApprove = "update friends set status = ".USER_APPROVED."
where requestId = ".$userId." and
providerId in (select Id from users where username in (".$friendNamesQueryPart."));
";
}
}
if (isset($_REQUEST['discardedFriends']))
{
$friendNames = split(",", $_REQUEST['discardedFriends']);
$friendCount = count($friendNames);
$friendNamesQueryPart = NULL;
for ($i = 0; $i < $friendCount; $i++)
{
if (strlen($friendNames[$i]) > 0)
{
if ($i > 0 )
{
$friendNamesQueryPart .= ",";
}
$friendNamesQueryPart .= "'".$friendNames[$i]."'";
}
}
if ($friendNamesQueryPart != NULL)
{
$sqlDiscard = "delete from friends
where requestId = ".$userId." and
providerId in (select Id from users where username in (".$friendNamesQueryPart."));
";
}
}
if ( ($sqlApprove != NULL ? $db->query($sqlApprove) : true) &&
($sqlDiscard != NULL ? $db->query($sqlDiscard) : true)
)
{
$out = SUCCESSFUL;
}
else
{
$out = FAILED;
}
}
else
{
$out = FAILED;
}
break;
default:
$out = FAILED;
break;
}
echo $out;
///////////////////////////////////////////////////////////////
function authenticateUser($db, $username, $password)
{
$sql22 = "select * from users
where username = '".$username."' and password = '".$password."'
limit 1";
$out = NULL;
if ($result22 = $db->query($sql22))
{
if ($row22 = $db->fetchObject($result22))
{
$out = $row22->Id;
$sql22 = "update users set authenticationTime = NOW(),
IP = '".$_SERVER["REMOTE_ADDR"]."' ,
port = 15145
where Id = ".$row22->Id."
limit 1";
$db->query($sql22);
}
}
return $out;
}
?>
现在我想从我的数据库中选择一个随机用户。 我知道如何做应用程序部分，但正如我已经说过的，我不知道如何做服务器部分。 有人可以告诉我这是怎么回事吗？
答案 0 :(得分：2)
试试这个：
SELECT username
FROM users
ORDER BY RAND()
LIMIT 1
此查询将从username表中随机选择users。
修改
如果您的表包含数千条记录，则RAND()不是一个好主意。另一种选择是：
使用MAX(userid)查找用户名的最大ID。
选择一个小于php中最大id的随机数。
使用随机数查询记录。像：
SELECT username
FROM users
WHERE userid='$randnum'
此方法会更快，因为它查询常量值。
答案 1 :(得分：-1)
这会给你一个随机的5位数字符串。您可以通过更改此方案中的最后一位数字（5）来修改长度。
$RandNumber = substr( md5(rand()), 0, 5);