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 = 35 
WHERE 
  cscart_products_categories.product_id IN (
    1947, 1458, 1460, 1464, 1455, 1382, 1385, 
    1383, 1386, 25, 1758, 1757, 1734, 1254, 
    1684, 1379, 1378, 1792, 1791, 1793, 
    1789, 1716, 1714, 1715, 1720, 1719, 
    1722, 1713, 1718, 1717, 1867, 1721, 
    1685, 1207, 1210, 1203, 1389, 1188, 
    1190, 1209, 1186, 1852, 1456, 1457, 
    1045, 1046, 1187, 1577
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00194

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": 48,
      "filtered": 100,
      "index_condition": "cscart_products_categories.product_id in (1947,1458,1460,1464,1455,1382,1385,1383,1386,25,1758,1757,1734,1254,1684,1379,1378,1792,1791,1793,1789,1716,1714,1715,1720,1719,1722,1713,1718,1717,1867,1721,1685,1207,1210,1203,1389,1188,1190,1209,1186,1852,1456,1457,1045,1046,1187,1577)"
    },
    "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
    }
  }
}