SELECT 
  cscart_products_categories.product_id, 
  GROUP_CONCAT(
    IF(
      cscart_products_categories.link_type = "M", 
      CONCAT(
        cscart_products_categories.category_id, 
        "M"
      ), 
      cscart_products_categories.category_id
    )
  ) AS category_ids, 
  product_position_source.position AS position 
FROM 
  cscart_products_categories 
  INNER JOIN cscart_categories ON cscart_categories.category_id = cscart_products_categories.category_id 
  AND cscart_categories.storefront_id IN (0, 1) 
  AND (
    cscart_categories.usergroup_ids = '' 
    OR FIND_IN_SET(
      0, cscart_categories.usergroup_ids
    ) 
    OR FIND_IN_SET(
      1, cscart_categories.usergroup_ids
    )
  ) 
  AND cscart_categories.status IN ('A', 'H') 
  LEFT JOIN cscart_products_categories AS product_position_source ON cscart_products_categories.product_id = product_position_source.product_id 
  AND product_position_source.category_id = 265 
WHERE 
  cscart_products_categories.product_id IN (
    10320, 10321, 10322, 9690, 10106, 10105, 
    10104, 10103, 10206, 10209, 10216, 
    10203, 10204, 10205, 10207, 10208, 
    10210, 10211, 10212, 10213, 10214, 
    10215, 10217, 10218, 10219, 10220, 
    10221, 10222, 10323, 10324, 10325, 
    10326, 10327, 10328, 10329, 10330, 
    10331, 10332, 10333, 10334, 10335, 
    10336, 10337, 10338, 10339, 10340, 
    10341, 10342, 10778, 10779, 10780, 
    10781, 10782, 10783, 10784, 10785, 
    10786, 10787, 10788, 10789, 10790, 
    10791, 9688, 10792
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00134

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_products_categories",
      "access_type": "range",
      "possible_keys": ["PRIMARY", "pt"],
      "key": "pt",
      "key_length": "3",
      "used_key_parts": ["product_id"],
      "rows": 64,
      "filtered": 100,
      "index_condition": "cscart_products_categories.product_id in (10320,10321,10322,9690,10106,10105,10104,10103,10206,10209,10216,10203,10204,10205,10207,10208,10210,10211,10212,10213,10214,10215,10217,10218,10219,10220,10221,10222,10323,10324,10325,10326,10327,10328,10329,10330,10331,10332,10333,10334,10335,10336,10337,10338,10339,10340,10341,10342,10778,10779,10780,10781,10782,10783,10784,10785,10786,10787,10788,10789,10790,10791,9688,10792)"
    },
    "table": {
      "table_name": "product_position_source",
      "access_type": "eq_ref",
      "possible_keys": ["PRIMARY", "pt"],
      "key": "PRIMARY",
      "key_length": "6",
      "used_key_parts": ["category_id", "product_id"],
      "ref": [
        "const",
        "noframes_angrybeaver.cscart_products_categories.product_id"
      ],
      "rows": 1,
      "filtered": 100
    },
    "table": {
      "table_name": "cscart_categories",
      "access_type": "eq_ref",
      "possible_keys": ["PRIMARY", "c_status", "p_category_id"],
      "key": "PRIMARY",
      "key_length": "3",
      "used_key_parts": ["category_id"],
      "ref": ["noframes_angrybeaver.cscart_products_categories.category_id"],
      "rows": 1,
      "filtered": 100,
      "attached_condition": "cscart_categories.storefront_id in (0,1) and (cscart_categories.usergroup_ids = '' or find_in_set(0,cscart_categories.usergroup_ids) or find_in_set(1,cscart_categories.usergroup_ids)) and cscart_categories.`status` in ('A','H')"
    }
  }
}