sql-forespørgsel for at bestemme de mest lignende varer ved tags

Denne forespørgsel returnerer alle elementer, der har det maksimale antal tags til fælles:

SET @item = 1;

SELECT
  goods_id
FROM
  links
WHERE
  tag_id IN (SELECT tag_id FROM links WHERE example@sqldat.com)
  AND example@sqldat.com
GROUP BY
  goods_id
HAVING
  COUNT(*) = (
    SELECT
      COUNT(*)
    FROM
      links
    WHERE
      tag_id IN (SELECT tag_id FROM links WHERE example@sqldat.com)
      AND example@sqldat.com
    GROUP BY
      goods_id
    ORDER BY
      COUNT(*) DESC
    LIMIT 1
  )

Se venligst violin her .

Eller denne vil returnere alle varer, selv dem uden fælles tags, sorteret efter antallet af fælles tags:

SELECT
  goods_id
FROM
  links
WHERE
  example@sqldat.com
GROUP BY
  goods_id
ORDER BY
  COUNT(CASE WHEN tag_id IN (SELECT tag_id FROM links WHERE example@sqldat.com) THEN 1 END) DESC;