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 = 7 
WHERE 
  cscart_products_categories.product_id IN (
    681, 393, 41, 1827, 1454, 1476, 1473, 
    1198, 1179, 1281, 926, 1258, 1168, 1394, 
    1259, 1865, 390, 1412, 1066, 1399, 1204, 
    1387, 332, 330, 333, 329, 327, 504, 1008, 
    758, 1817, 1819, 1172, 1196, 1908, 1809, 
    1405, 1851, 730, 1481, 382, 453, 425, 
    1428, 1425, 1426, 1430, 1429
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00217

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": 49,
      "filtered": 100,
      "index_condition": "cscart_products_categories.product_id in (681,393,41,1827,1454,1476,1473,1198,1179,1281,926,1258,1168,1394,1259,1865,390,1412,1066,1399,1204,1387,332,330,333,329,327,504,1008,758,1817,1819,1172,1196,1908,1809,1405,1851,730,1481,382,453,425,1428,1425,1426,1430,1429)"
    },
    "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": ["bacpvdev_db.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')"
    },
    "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", "bacpvdev_db.cscart_products_categories.product_id"],
      "rows": 1,
      "filtered": 100
    }
  }
}