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 (
    12650, 12649, 12643, 12640, 12647, 15800, 
    12639, 12641, 12638, 12637, 12634, 
    12635, 12636, 12654, 12653, 12652, 
    12656, 12655, 12646, 12631, 12998, 
    12997, 12996, 12995, 10826, 10825, 
    10824, 10823, 10822, 10821, 10820, 
    10819, 10818, 10817, 10816, 10815, 
    10814, 10813, 13044, 13043, 13042, 
    13041, 13040, 13039, 13038, 13037, 
    13036, 13035, 13034, 13033, 13032, 
    13031, 13030, 13029, 13028, 13027, 
    13026, 13025, 13024, 13023, 13022, 
    13021, 13020, 13019
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00105

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": 98,
      "filtered": 100,
      "index_condition": "cscart_products_categories.product_id in (12650,12649,12643,12640,12647,15800,12639,12641,12638,12637,12634,12635,12636,12654,12653,12652,12656,12655,12646,12631,12998,12997,12996,12995,10826,10825,10824,10823,10822,10821,10820,10819,10818,10817,10816,10815,10814,10813,13044,13043,13042,13041,13040,13039,13038,13037,13036,13035,13034,13033,13032,13031,13030,13029,13028,13027,13026,13025,13024,13023,13022,13021,13020,13019)"
    },
    "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')"
    }
  }
}