タグによって最も類似した商品を判別するためのSQLクエリ

このクエリは、共通のタグの最大数を持つすべてのアイテムを返します：

SET @item = 1;

SELECT
  goods_id
FROM
  links
WHERE
  tag_id IN (SELECT tag_id FROM links WHERE [email protected])
  AND [email protected]
GROUP BY
  goods_id
HAVING
  COUNT(*) = (
    SELECT
      COUNT(*)
    FROM
      links
    WHERE
      tag_id IN (SELECT tag_id FROM links WHERE [email protected])
      AND [email protected]
    GROUP BY
      goods_id
    ORDER BY
      COUNT(*) DESC
    LIMIT 1
  )

フィドルこちら をご覧ください。 。

または、これは、共通のタグがないものも含めて、共通の説明のタグの数順に並べられたすべてのアイテムを返します。

SELECT
  goods_id
FROM
  links
WHERE
  [email protected]
GROUP BY
  goods_id
ORDER BY
  COUNT(CASE WHEN tag_id IN (SELECT tag_id FROM links WHERE [email protected]) THEN 1 END) DESC;