php - 我的 php 脚本在执行返回零 (0) 行的 mysql 选择查询后停止处理和输出

Question

下面是我的代码。当我尝试插入已存在的用户时，查询返回一行并且脚本工作正常。但是当查询返回零 row 时，脚本会在下面代码中注释为“STOPS HERE”的点处停止。请我真的不明白这个问题，而且我是 php 新手。甚至 if 之外的 echo 语句也不会被执行。

<?php
session_start();
$_SESSION["error"] = "";
include "dbconnection.php";

$_SESSION["validUser"] = 4; 

$validUser = $_SESSION["validUser"];


extract($_POST);

if($courseSession == ""){
    echo "You must Select a course session ";   
}
else {
    $query = "SELECT * FROM courses WHERE student = $validUser AND course='$courseSession'";
    $result = mysql_query($query, $db)  or die(mysql_error($db));

    if(!$result){
        echo " no results have been returned testing "; // used for testing
    }
    else {
        echo " Results returned but don't understand  \n Number rows = ";   // used for testing
        echo mysql_num_rows($result);

    } //STOPS HERE, here is where the script stops after query above returns 0 row.
    $check = mysql_num_rows($result)   or die(mysql_error($db));

    echo " after check course ";
    if($check){

        echo "You have already registered for this session "; 


    }

    else if(!$check){

        $query = "INSERT INTO courses
                            (course, student, groupId)

                        VALUES
                            ('$courseSession', '$validUser', '$group')";

        $res = mysql_query($query, $db) or die(mysql_error($db));
        if(!$res){
            echo "Error Registering Course ";
        }
        else{
            echo "Successfully registered for this session ";
        }
    }
}


echo " TESting testing ";


?>

Answer 1

您的代码中的这一行有问题:

$check = mysql_num_rows($result) 或 die(mysql_error($db));。

当它运行时，mysql_num_rows($result) 返回 0，在这种情况下其计算结果与 false 相同，这就是为什么 die() 被执行但没有任何结果之后运行。