SELECT 
  ushop_products_categories.product_id, 
  GROUP_CONCAT(
    IF(
      ushop_products_categories.link_type = "M", 
      CONCAT(
        ushop_products_categories.category_id, 
        "M"
      ), 
      ushop_products_categories.category_id
    )
  ) AS category_ids 
FROM 
  ushop_products_categories 
  INNER JOIN ushop_categories ON ushop_categories.category_id = ushop_products_categories.category_id 
  AND ushop_categories.storefront_id IN (0, 1) 
  AND (
    ushop_categories.usergroup_ids = '' 
    OR FIND_IN_SET(
      0, ushop_categories.usergroup_ids
    ) 
    OR FIND_IN_SET(
      1, ushop_categories.usergroup_ids
    )
  ) 
  AND ushop_categories.status IN ('A', 'H') 
WHERE 
  ushop_products_categories.product_id IN (194) 
GROUP BY 
  ushop_products_categories.product_id

Query time 0.00039

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "table": {
          "table_name": "ushop_products_categories",
          "access_type": "ref",
          "possible_keys": ["PRIMARY", "pt"],
          "key": "pt",
          "key_length": "3",
          "used_key_parts": ["product_id"],
          "ref": ["const"],
          "rows": 1,
          "filtered": 100
        }
      },
      {
        "table": {
          "table_name": "ushop_categories",
          "access_type": "eq_ref",
          "possible_keys": ["PRIMARY", "c_status", "p_category_id"],
          "key": "PRIMARY",
          "key_length": "3",
          "used_key_parts": ["category_id"],
          "ref": ["ushop_shopping.ushop_products_categories.category_id"],
          "rows": 1,
          "filtered": 100,
          "attached_condition": "ushop_categories.storefront_id in (0,1) and (ushop_categories.usergroup_ids = '' or find_in_set(0,ushop_categories.usergroup_ids) or find_in_set(1,ushop_categories.usergroup_ids)) and ushop_categories.`status` in ('A','H')"
        }
      }
    ]
  }
}