Question

I have a product_table with a product_id among several other fields.

I am creating a tag_table with 2 fields, tag_id and tag_name.

The tags could be anything like "silver" or "penn state" etc.

I am also creating a product_tag_map table with product_id and tag_id in order to map a product to any number of tags.

If I wanted to create a category that contained all products tagged as "silver", "necklace", "diamond". But also exclude any product tagged as "initial", "journey"

(Obviously I would use the tag_id not tag_name, so products with tags [2,4,5] that do not have tags [3,6])

How could a create a temporary product table and populate it with the matching products?

update

here is my product_tag_map table:

CREATE TABLE `product_tag_map` (
 `product_tag_map_id` int(11) NOT NULL auto_increment,
 `tag_id` int(11) NOT NULL,
 `product_id` int(11) NOT NULL,
 PRIMARY KEY  (`product_tag_map_id`),
 UNIQUE KEY `tag_id` (`tag_id`,`product_id`),
 KEY `tag_id_2` (`tag_id`)
) ENGINE=MyISAM AUTO_INCREMENT=7897 DEFAULT CHARSET=utf8

Note: I am not using product_tag_map_id for anything. I am just in the habit of giving each table a primary key like so. So If I should remove it thats fine.

Answer 1

The question is, what would you need a temp table for? Why not query it directly?

SELECT
  p.product_id,
  p.product_name
FROM
  product_table p
WHERE
  EXISTS (
    SELECT 1 
      FROM product_tag_map 
     WHERE product_id = p.product_id AND tag_id IN (2,4,5)
  )
  AND NOT EXISTS (
    SELECT 1 
      FROM product_tag_map 
     WHERE product_id = p.product_id AND tag_id IN (3,6)
  )

Create appropriate indexes (one multi-column index over (product_tag_map.product_id, product_tag_map.tag_id) and one separate over (product_tag_map.tag_id), in addition to the “normal” PK/FK indexes) and this should be plenty fast.

---

EDIT: A cacheable (as far as query plans go) and more dynamic variant of the above would be:

Create a user_searches table (search_session_id, tag_id, include) with a multi_column index over (search_session_id, include) and a separate index over tag_id. Then fill it as the user selects criteria:

search_session_id   tag_id   include
              ...
             4711        2         1
             4711        4         1
             4711        5         1
             4711        3         0
             4711        6         0
              ...

And query like this:

SELECT
  p.product_id,
  p.product_name
FROM
  product_table p
WHERE
  EXISTS (
    SELECT 1 
      FROM product_tag_map m INNER JOIN user_searches s ON s.tag_id = m.tag_id
     WHERE m.product_id = p.product_id 
           AND s.search_session_id = 4711 /* this should be a parameter */
           AND s.include = 1
  )
  AND NOT EXISTS (
    SELECT 1 
      FROM product_tag_map m INNER JOIN user_searches s ON s.tag_id = m.tag_id
     WHERE m.product_id = p.product_id 
           AND s.search_session_id = 4711 /* this should be a parameter */
           AND s.include = 0

  )