php - php中mysql查询中的内联变量不起作用

Question

我有以下 php 代码，

<?php
    $subject_set = mysqli_query($db_link, 'SELECT * FROM subjects');

    if(!$subject_set){
        die("Database subjects query failed: ".mysql_error());
    }

    while ($subject=mysqli_fetch_array($subject_set)) {
        echo "<li>{$subject["menu_name"]}</li>";
            $page_set = mysqli_query($db_link, 'SELECT * FROM pages WHERE subject_id= {$subject["id"]}');
            // $page_set = mysqli_query($db_link, 'SELECT * FROM pages WHERE subject_id='.$subject["id"]);

            if(!$page_set){
                die("Database pages query failed: ".mysql_error());
            }

            echo "<ul class=\"pages\">";

            while ($page=mysqli_fetch_array($page_set)) {
                echo "<li>{$page["menu_name"]}</li>";
            }

            echo "</ul>";

        }
    ?>

当我运行这段代码时，当我得到 'page_set' 值时，它会给我一个错误。在行中 $page_set = mysqli_query($db_link, 'SELECT * FROM pages WHERE subject_id= {$subject["id"] }'); 但是我使用注释行而不是上面的行代码工作正常。此外，mysql_error() 没有向我显示错误。

Answer 1

http://docs.php.net/language.types.string说

Note: Unlike the double-quoted and heredoc syntaxes, variables and escape sequences for special characters will not be expanded when they occur in single quoted strings.