php - 从数据库中只查询 400 个字符是行不通的

Question

我有这行代码:

$query=$db->prepare("SELECT post_id, title, LEFT(body, 400), category FROM posts INNER JOIN categories ON categories.category_id=posts.category_id ORDER BY post_id DESC LIMIT $start, $per_page");

LEFT(body,400) 不会只查询 400 个字符，它会查询除最后一个单词以外的所有字符。这是我用来回应查询的代码(它在 while 循环中 w/db)

<p><?php
     $body_sub = substr($body, 0). "...<a href='post.php?id=$post_id'> Continue Reading →</a>";
    echo nl2br($body_sub);
?></p>

Answer 1

body 列在函数中使用后在技术上并不存在。您需要为该列起别名:

... LEFT(body, 400) AS body

然后调用body。

我还建议在系统术语周围使用反引号，例如列:

SELECT `post_id`, 
       `title`, 
       LEFT(`body`, 400) AS `body`, 
       `category`
FROM   `posts`
       INNER JOIN `categories` 
               ON `categories`.`category_id` = `posts`.`category_id` 
ORDER  BY `post_id` DESC 
LIMIT  $start, $per_page