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 = 305 
WHERE 
  cscart_products_categories.product_id IN (
    435351, 456510, 404001, 413818, 442117, 
    433550, 450230, 439049, 414690, 448070, 
    414544, 431904, 404473, 422990, 448236, 
    413068, 425901, 407405, 406178, 437072, 
    430766, 447574, 460572, 460325, 406193, 
    451309, 446162, 438117, 439044, 406083, 
    415033, 460158, 422354, 409660, 453640, 
    424754, 410340, 417422, 422439, 422004, 
    421990, 446415, 436834, 440447, 410009, 
    439533, 411516, 442635
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00121

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost": 0.243691242,
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_products_categories",
          "access_type": "range",
          "possible_keys": ["PRIMARY", "pt"],
          "key": "pt",
          "key_length": "3",
          "used_key_parts": ["product_id"],
          "loops": 1,
          "rows": 48,
          "cost": 0.08683616,
          "filtered": 100,
          "attached_condition": "cscart_products_categories.product_id in (435351,456510,404001,413818,442117,433550,450230,439049,414690,448070,414544,431904,404473,422990,448236,413068,425901,407405,406178,437072,430766,447574,460572,460325,406193,451309,446162,438117,439044,406083,415033,460158,422354,409660,453640,424754,410340,417422,422439,422004,421990,446415,436834,440447,410009,439533,411516,442635)",
          "using_index": true
        }
      },
      {
        "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": ["u985510652_ecartify.cscart_products_categories.category_id"],
          "loops": 48,
          "rows": 1,
          "cost": 0.04375232,
          "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",
            "u985510652_ecartify.cscart_products_categories.product_id"
          ],
          "loops": 48,
          "rows": 1,
          "cost": 0.08225472,
          "filtered": 100
        }
      }
    ]
  }
}