MySQL：抓取在另一个表中找不到ID的行

Question

Hope this makes sense, bad at this.

Here's the problem: I am trying to get a list of posts from an "articles" table and each article has a list of tags associated with them in another table called it "article_category_reference".

Users block certain tags to customize their feed, so I want to filter them out of course. These will be in an array like (12 and 19 being tag ids):

$in = [0 => 12, 1 => 19];

Here's the current sample MySQL:

SELECT a.`article_id`,
       a.`title`,
       a.`text`
FROM   `articles` a
       LEFT JOIN `article_category_reference` r
              ON r.article_id = a.article_id
WHERE  r.category_id NOT IN ( ?,? )
ORDER  BY a.`date` DESC
LIMIT  ?, ?  

My problem is, it will filter out articles if they only have a single tag so I have it completely wrong. I guess I can't simply join a table like that to filter?

Answer 1

You can perform a nested query. Very useful on Mysql

SELECT a.`article_id`,
   a.`title`,
   a.`text`
FROM   `articles` a
   WHERE a.article_id IN ( 
         SELECT r.`article_id` 
         FROM `article_category_reference` r
         WHERE  r.category_id NOT IN ( ?,? )
);

In simple terms go to article_category_reference get the all the ids but these and use these ids to query the articles table.

Answer 2

You could simply construct the query using a comma separated list of the values that you want to filter out, ie:

WHERE  r.category_id NOT IN ( 12, 19 )

I don't understand the part though where you say that

it will filter out articles if they only have a single tag

Maybe you could show a complete example with query, sample data, the result that you are getting and the result that you are expecting if this does not answer your question.