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 (
    10456, 10455, 12702, 10446, 12579, 12580, 
    12700, 10444, 10443, 10442, 10441, 
    10440, 10439, 10438, 10437, 10436, 
    10435, 10434, 10433, 10432, 10431, 
    10430, 10429, 10428, 10427, 10426, 
    10425, 12564, 10424, 10423, 10422, 
    10421, 10420, 10419, 10418, 10417, 
    12856, 10416, 10415, 10414, 12855, 
    12854, 12853, 10412, 10411, 10410, 
    10409, 10408, 10407, 10406, 15781, 
    10405, 10404, 10403, 10402, 10401, 
    10400, 10399, 10398, 10397, 10395, 
    10394, 10393, 10392
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00760

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": 70,
      "filtered": 100,
      "index_condition": "cscart_products_categories.product_id in (10456,10455,12702,10446,12579,12580,12700,10444,10443,10442,10441,10440,10439,10438,10437,10436,10435,10434,10433,10432,10431,10430,10429,10428,10427,10426,10425,12564,10424,10423,10422,10421,10420,10419,10418,10417,12856,10416,10415,10414,12855,12854,12853,10412,10411,10410,10409,10408,10407,10406,15781,10405,10404,10403,10402,10401,10400,10399,10398,10397,10395,10394,10393,10392)"
    },
    "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')"
    }
  }
}