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 (
    19860, 19820, 19863, 19865, 19866, 20154, 
    19868, 19869, 19870, 19871, 19872, 
    19873, 19875, 19874, 19876, 20087, 
    19877, 19878, 19879, 19880, 19881, 
    19882, 19883, 19884, 19885, 19886, 
    19888, 19889, 19890, 19891, 19892, 
    19893, 19894, 19895, 19896, 19897, 
    19898, 19899, 19900, 19901, 19902, 
    19903, 19904, 19905, 19925, 19906, 
    19907, 19908, 19909, 19910, 19911, 
    20576, 20088, 20089, 20091, 20092, 
    20093, 20094, 18661, 18662, 19131, 
    18664, 20724, 20725, 20728, 20955, 
    20956, 20957, 20958, 20959, 22277, 
    20971, 21078, 21102, 20972, 20973, 
    20974, 21103, 21923, 21924, 21925, 
    21926, 19867, 20065, 19887, 21749, 
    20723, 20726, 20727
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00122

JSON explain

{
  "query_block": {
    "select_id": 1,
    "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"],
          "rows": 89,
          "filtered": 100,
          "index_condition": "cscart_products_categories.product_id in (19860,19820,19863,19865,19866,20154,19868,19869,19870,19871,19872,19873,19875,19874,19876,20087,19877,19878,19879,19880,19881,19882,19883,19884,19885,19886,19888,19889,19890,19891,19892,19893,19894,19895,19896,19897,19898,19899,19900,19901,19902,19903,19904,19905,19925,19906,19907,19908,19909,19910,19911,20576,20088,20089,20091,20092,20093,20094,18661,18662,19131,18664,20724,20725,20728,20955,20956,20957,20958,20959,22277,20971,21078,21102,20972,20973,20974,21103,21923,21924,21925,21926,19867,20065,19887,21749,20723,20726,20727)"
        }
      },
      {
        "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": ["lillyshop_lillyshop.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')"
        }
      }
    ]
  }
}