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 (
    449431, 449270, 449272, 449290, 449318, 
    449330, 449341, 449357, 449173, 449180, 
    449188, 449225, 449250, 449259, 449083, 
    449116, 448973, 448976, 448981, 448994, 
    448864, 448865, 448874, 448890, 448920, 
    448947, 448955, 448773, 448808, 448826, 
    448827, 448830, 448854, 448666, 448707, 
    448732, 448738, 448743, 448749, 448572, 
    448581, 448596, 448614, 448643, 448467, 
    448480, 448483, 448492, 448501, 448534, 
    448544, 448556, 448366, 448416, 448426, 
    448430, 448446, 448265, 448300, 448310, 
    448314, 448329, 448333, 448348, 448349, 
    448162, 448196, 448198, 448216, 448236, 
    448252, 448255, 448259, 448070, 448084, 
    448121, 448141, 448150, 448158, 447976, 
    447990, 447998, 448009, 448015, 448042, 
    447863, 447887, 447891, 447927, 447950, 
    447951, 447767, 447785, 447845, 447859, 
    447661
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00088

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost": 0.321518524,
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_products_categories",
          "access_type": "range",
          "possible_keys": ["PRIMARY", "pt"],
          "key": "pt",
          "key_length": "3",
          "used_key_parts": ["product_id"],
          "loops": 1,
          "rows": 96,
          "cost": 0.1728812,
          "filtered": 100,
          "attached_condition": "cscart_products_categories.product_id in (449431,449270,449272,449290,449318,449330,449341,449357,449173,449180,449188,449225,449250,449259,449083,449116,448973,448976,448981,448994,448864,448865,448874,448890,448920,448947,448955,448773,448808,448826,448827,448830,448854,448666,448707,448732,448738,448743,448749,448572,448581,448596,448614,448643,448467,448480,448483,448492,448501,448534,448544,448556,448366,448416,448426,448430,448446,448265,448300,448310,448314,448329,448333,448348,448349,448162,448196,448198,448216,448236,448252,448255,448259,448070,448084,448121,448141,448150,448158,447976,447990,447998,448009,448015,448042,447863,447887,447891,447927,447950,447951,447767,447785,447845,447859,447661)",
          "using_index": true
        }
      },
      {
        "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": ["u985510652_ecartify.cscart_products_categories.category_id"],
          "loops": 96,
          "rows": 1,
          "cost": 0.08668544,
          "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')"
        }
      }
    ]
  }
}