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 
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') 
WHERE 
  cscart_products_categories.product_id IN (
    1501, 1487, 1498, 1497, 1496, 1491, 1495, 
    1493, 1486, 1489, 1488, 1485, 1459, 
    1477, 1484, 1483, 1482, 1480, 1481, 
    1474, 1479, 1478, 1465, 1475, 1476, 
    1473, 1276, 1463, 1471, 1462, 1267, 
    1460, 820, 1472, 1464, 1470, 1469, 1468, 
    1467, 1466, 1461, 1458, 1457, 1456, 
    1455, 1454, 1446, 1450
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00171

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 (1501,1487,1498,1497,1496,1491,1495,1493,1486,1489,1488,1485,1459,1477,1484,1483,1482,1480,1481,1474,1479,1478,1465,1475,1476,1473,1276,1463,1471,1462,1267,1460,820,1472,1464,1470,1469,1468,1467,1466,1461,1458,1457,1456,1455,1454,1446,1450)"
    },
    "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')"
    }
  }
}