匹配查询中数组的元素

Question

I want to select a post only if $arr_tags match all array_elements with tags_is_tags . For example in this situation will be outputted 0 posts because one array element didn't match with tags_id_tags

How can i do something like that ?

$arr_tags = array("16", "17", "36", "543"); // the dimension is not always the same

post_id_post        tags_id_tags    
    282                      16     
    282                      17     
    282                      36 
    282                      546 

I have this code but the query is not finished.

            $sql = $db -> prepare("
                SELECT post_id_post 
                FROM posts
                // ...
            ");

            $sql -> bind_param('s', $val);
            $sql -> execute();
            $sql -> bind_result($d_post);

Thanks for your time

Answer 1

  SELECT post_id_post
    FROM posts
   WHERE tags_id_tags IN ("16", "17", "36", "543")
GROUP BY post_id_post
  HAVING COUNT(*) = 4

You put all the required tags' IDs in the IN clause and change the number in COUNT(*) = 4 expression to the number of tags passed

Answer 2

It seems to me that as much as anything you want to know how to ask the right question. The magic words here are "relational division".

It is one of the operators in Codd 's relational algebra and there have been several variations proposed since. Most recently, Chris Date has proposed replacing the whole concept with image relations .

SQL has no explicit divide operator. There are a number of workarounds using other operator and the most appropriate will depend on your requirements, including exact division or division with remainder and how to handle an empty divisor. Then there are the usual considerations: SQL product and version, performance, personal style and taste, etc.

Here are a couple of articles which should help you with these choices:

On Making Relational Division Comprehensible

Divided We Stand: The SQL of Relational Division