Question

我有一个noob问题，但我没有在网上找到任何答案，因为这是我认为的一些特殊问题。我正在使用自动刷新编写消息系统。

这是为了获取db中的最新ID：

$query = mysql_query("SELECT * FROM `messages` 
                          WHERE `requestor`='".$_POST['user_id']."' 
                          AND `target`='".$_POST['target_id']."' 
                          OR `requestor`='".$_POST['target_id']."' 
                          AND `target`='".$_POST['user_id']."' 
                          ORDER BY `id` ASC");
$rows = mysql_fetch_array($query);
$id = $rows['id'];      //latest message id at this moment

$lastSeenID = $_POST['msg_id'];     //This is the latest id which is shown on the client

现在我需要ID大于客户端上最后一个已知id的列。（$ lastSeenID）。

但这不会以正确的方式运作。

mysql_query("SELECT * FROM `messages` 
             WHERE `id` > '".$lastSeenID."' 
             AND `requestor`='".$_POST['user_id']."' 
             AND `target`='".$_POST['target_id']."' 
             OR `requestor`='".$_POST['target_id']."' 
             AND `target`='".$_POST['user_id']."' 
             ORDER BY `id` ASC")

我希望你能帮助我。

Answer 1

请开始喜欢查询参数：

<?php
$mysqli = new mysqli("localhost", "my_user", "my_password", "world");

/* check connection */
if (mysqli_connect_errno()) {
    printf("Connect failed: %s\n", mysqli_connect_error());
    exit();
}

$city = "Amersfoort";

/* create a prepared statement */
if ($stmt = $mysqli->prepare("SELECT District FROM City WHERE Name=?")) {

    /* bind parameters for markers */
    $stmt->bind_param("s", $city);

    /* execute query */
    $stmt->execute();

    /* bind result variables */
    $stmt->bind_result($district);

    /* fetch value */
    $stmt->fetch();

    printf("%s is in district %s\n", $city, $district);

    /* close statement */
    $stmt->close();
}

/* close connection */
$mysqli->close();
?>

Answer 2

试试这个：

mysql_query("SELECT * FROM `messages` WHERE (`id` > '$lastSeenID' AND `requestor`='$_POST['user_id']' AND `target`='$_POST['target_id']' OR `requestor`='$_POST['target_id']' AND `target`='$_POST['user_id']') ORDER BY `id` ASC");

或MySQLi

mysqli_query($con,"SELECT * FROM `messages` WHERE (`id` > '$lastSeenID' AND `requestor`='$_POST['user_id']' AND `target`='$_POST['target_id']' OR `requestor`='$_POST['target_id']' AND `target`='$_POST['user_id']') ORDER BY `id` ASC");

Answer 3

代表OP发表。

我得到了工作代码（感谢括号中的建议）。

mysql_query("SELECT * FROM `messages` WHERE (`id` > '".$lastSeenID."' AND `requestor`='".$_POST['user_id']."' AND `target`='".$_POST['target_id']."') OR (`id` > '".$lastSeenID."' AND `requestor`='".$_POST['target_id']."' AND `target`='".$_POST['user_id']."') ORDER BY `id` ASC");

在PHP中使用OR的长MySQL语句？

3 个答案: