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 (
    12944, 10043, 10044, 10045, 10046, 10047, 
    10048, 10050, 10051, 10052, 10054, 
    10055, 10056, 10057, 10058, 10059, 
    10060, 10061, 10062, 10063, 10064, 
    10065, 10066, 10067, 10068, 10069, 
    10070, 10071, 10072, 10024, 10025, 
    10026, 10027, 10028, 10029, 10030, 
    10031, 10032, 10033, 10034, 10035, 
    10036, 10037, 10038, 10039, 10040, 
    9984, 9985, 9986, 9987, 9988, 9989, 
    9990, 9991, 9992, 9993, 9994, 9995, 
    9996, 9997, 9998, 9999, 9972, 9973
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00126

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": 64,
      "filtered": 100,
      "index_condition": "cscart_products_categories.product_id in (12944,10043,10044,10045,10046,10047,10048,10050,10051,10052,10054,10055,10056,10057,10058,10059,10060,10061,10062,10063,10064,10065,10066,10067,10068,10069,10070,10071,10072,10024,10025,10026,10027,10028,10029,10030,10031,10032,10033,10034,10035,10036,10037,10038,10039,10040,9984,9985,9986,9987,9988,9989,9990,9991,9992,9993,9994,9995,9996,9997,9998,9999,9972,9973)"
    },
    "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')"
    }
  }
}