PHP와 MySQL,이 함수의 문제점은 무엇입니까?

Question

이 함수는 작동하지 않으며 쿼리 내의 어딘가에 문제를 찾을 수 없습니다.

function get_category_posts($category, $page, $per_page) { 
$start = (int)($page - 1) * $per_page; 
$per_page = (int)$per_page; 

$sql = "SELECT 
    `posts`.`post_id` AS `id`, 
    `posts`.`post_title` AS `title`, 
    `posts`.`post_category` AS `category`, 
    `posts`.`post_body` AS `preview`, 
    `posts`.`post_user` AS `user`, 
    DATE_FORMAT(`posts`.`post_date`, '%Y-%m-%d %H:%i:%s') AS `date`, 
    `comments`.`total_comments`, 
    DATE_FORMAT(`comments`.`last_comment`, '%Y-%m-%d %H:%i:%s') AS `last_comment` 
FROM `posts` 
WHERE `category`='".$category."' 
LEFT JOIN (
    SELECT 
     `post_id`, 
     COUNT(`comment_id`) AS `total_comments`, 
     MAX(`comment_date`) AS `last_comment` 
    FROM `comments` 
    GROUP BY `post_id` 
) AS `comments` 
ON `posts`.`post_id` = `comments`.`post_id` 
ORDER BY `posts`.`post_date` DESC 
LIMIT {$start}, {$per_page}"; 

$posts = mysql_query($sql); 
//die(mysql_error()); 

$rows = array(); 
while (($row = mysql_fetch_assoc($posts)) !== false) { 
    $rows[] = array(
     'id' => $row['id'], 
     'title' => html_entity_decode($row['title']), 
     'category' => html_entity_decode($row['category']), 
     'preview' => html_entity_decode($row['preview']), 
     'user' => html_entity_decode($row['user']), 
     'date' => $row['date'], 
     'total_comments' => ($row['total_comments'] === null) ? 0 : $row['total_comments'], 
     'last_comment' => ($row['last_comment'] === null) ? 'aldrig' : $row['last_comment'] 
     ); 
} 

return $rows; 

} 기능은 그것과는

당신은 당신의 SQL 구문에 오류가 반환하지만, WHERE 카테고리 ='".$category."'없이 잘 작동; 사용할 수있는 권리 구문에 대한 MySQL 서버 버전에 해당하는 설명서를 확인 근처 줄에서 'LEFT JOIN (total_comments AS post_id, COUNT (comment_id)을 선택'테이블 조인 후 절이 와야 (12)

Answer 1

여기서 '에 "알 수없는 열'카테고리 '와 BY ORDER 및 LIMIT 전에

SELECT <column list> 
FROM <table> 
JOIN <table> USING (<column>) 
WHERE <condition> 
OR <condition> 
AND <condition> 
GROUP BY <column list> 
HAVING <expression> 

Answer 2

는 조건

$sql = "SELECT 
    `posts`.`post_id` AS `id`, 
    `posts`.`post_title` AS `title`, 
    `posts`.`post_category` AS `category`, 
    `posts`.`post_body` AS `preview`, 
    `posts`.`post_user` AS `user`, 
    DATE_FORMAT(`posts`.`post_date`, '%Y-%m-%d %H:%i:%s') AS `date`, 
    `comments`.`total_comments`, 
    DATE_FORMAT(`comments`.`last_comment`, '%Y-%m-%d %H:%i:%s') AS `last_comment` 
FROM `posts` 
LEFT JOIN (
    SELECT 
     `post_id`, 
     COUNT(`comment_id`) AS `total_comments`, 
     MAX(`comment_date`) AS `last_comment` 
    FROM `comments` 
    GROUP BY `post_id` 
) AS `comments` 
ON `posts`.`post_id` = `comments`.`post_id` 
WHERE `posts`.`category`='".$category."' 
ORDER BY `posts`.`post_date` DESC 
LIMIT {$start}, {$per_page}";