April 18, 2012
PHP and MySQL, what's wrong with this function?
Question by Peter Jonsson
This function doesn’t work and I can’t find the problem, which is somewhere inside the query.
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 $rows;
}
The function works fine without the WHEREcategory='".$category."', however, with it it returns
You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ‘LEFT JOIN ( SELECT
post_id, COUNT(comment_id) AStotal_comments, ‘ at line 12
Answer by Mikey
The WHERE clause must come after the table joins and before the ORDER BY and LIMIT
SELECT <column list>
FROM <table>
JOIN <table> USING (<column>)
WHERE <condition>
OR <condition>
AND <condition>
GROUP BY <column list>
HAVING <expression>
Answer by Starx
JOINs have to come before WHERE condition
$sql = "SELECT
`posts`.`post_id` AS `id`,
`posts`.`post_title` AS `title`,
`posts`.`post_category` AS `category`,
`posts`.`post_body` AS `preview`,
`posts`.`post_user` AS `user`,
DATE_FORMAT(`posts`.`post_date`, '%Y-%m-%d %H:%i:%s') AS `date`,
`comments`.`total_comments`,
DATE_FORMAT(`comments`.`last_comment`, '%Y-%m-%d %H:%i:%s') AS `last_comment`
FROM `posts`
LEFT JOIN (
SELECT
`post_id`,
COUNT(`comment_id`) AS `total_comments`,
MAX(`comment_date`) AS `last_comment`
FROM `comments`
GROUP BY `post_id`
) AS `comments`
ON `posts`.`post_id` = `comments`.`post_id`
WHERE `posts`.`category`='".$category."'
ORDER BY `posts`.`post_date` DESC
LIMIT {$start}, {$per_page}";
