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 (
    10615, 10614, 10613, 10612, 10611, 10610, 
    10609, 10608, 10607, 10600, 10599, 
    10598, 10597, 10596, 15952, 15951, 
    15950, 15949, 15947, 15946, 15945, 
    15944, 10583, 10582, 10581, 10580, 
    10579, 10578, 10577, 10576, 10575, 
    10573, 10572, 10569, 10568, 10567, 
    10566, 10565, 10563, 10561, 10560, 
    10558, 10557, 10556, 10552, 10551, 
    10550, 15943, 10545, 10544, 10543, 
    10542, 10541, 10540, 10539, 10538, 
    10537, 10536, 10535, 10534, 10533, 
    10532, 10531, 10530
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00076

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": 91,
      "filtered": 100,
      "index_condition": "cscart_products_categories.product_id in (10615,10614,10613,10612,10611,10610,10609,10608,10607,10600,10599,10598,10597,10596,15952,15951,15950,15949,15947,15946,15945,15944,10583,10582,10581,10580,10579,10578,10577,10576,10575,10573,10572,10569,10568,10567,10566,10565,10563,10561,10560,10558,10557,10556,10552,10551,10550,15943,10545,10544,10543,10542,10541,10540,10539,10538,10537,10536,10535,10534,10533,10532,10531,10530)"
    },
    "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": ["noframes_angrybeaver.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')"
    }
  }
}