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 (
    39503, 40547, 40112, 40580, 40714, 40836, 
    40232, 40208, 40469, 40616, 40738, 
    40088, 40374, 40787, 40679, 40516, 
    40350, 40812, 40762, 40160, 40326, 
    40422, 40136, 40302, 39585, 40901, 
    40896, 40861, 40865, 40893, 40874, 
    40862, 40873, 40877, 40884, 40887, 
    40891, 40892, 40890, 40883, 40889, 
    40869, 40864, 40880, 40870, 40871, 
    40872, 40875, 40876, 40867, 40879, 
    40886, 40866, 40885, 40888
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00186

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "94.56"
    },
    "grouping_operation": {
      "using_filesort": false,
      "nested_loop": [
        {
          "table": {
            "table_name": "cscart_products_categories",
            "access_type": "range",
            "possible_keys": [
              "PRIMARY",
              "pt"
            ],
            "key": "pt",
            "used_key_parts": [
              "product_id"
            ],
            "key_length": "3",
            "rows_examined_per_scan": 101,
            "rows_produced_per_join": 101,
            "filtered": "100.00",
            "index_condition": "(`cscartdb`.`cscart_products_categories`.`product_id` in (39503,40547,40112,40580,40714,40836,40232,40208,40469,40616,40738,40088,40374,40787,40679,40516,40350,40812,40762,40160,40326,40422,40136,40302,39585,40901,40896,40861,40865,40893,40874,40862,40873,40877,40884,40887,40891,40892,40890,40883,40889,40869,40864,40880,40870,40871,40872,40875,40876,40867,40879,40886,40866,40885,40888))",
            "cost_info": {
              "read_cost": "49.11",
              "eval_cost": "10.10",
              "prefix_cost": "59.21",
              "data_read_per_join": "1K"
            },
            "used_columns": [
              "product_id",
              "category_id",
              "link_type"
            ]
          }
        },
        {
          "table": {
            "table_name": "cscart_categories",
            "access_type": "eq_ref",
            "possible_keys": [
              "PRIMARY",
              "c_status",
              "p_category_id"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "category_id"
            ],
            "key_length": "3",
            "ref": [
              "cscartdb.cscart_products_categories.category_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 5,
            "filtered": "5.00",
            "cost_info": {
              "read_cost": "25.25",
              "eval_cost": "0.51",
              "prefix_cost": "94.56",
              "data_read_per_join": "16K"
            },
            "used_columns": [
              "category_id",
              "storefront_id",
              "usergroup_ids",
              "status"
            ],
            "attached_condition": "((`cscartdb`.`cscart_categories`.`storefront_id` in (0,1)) and ((`cscartdb`.`cscart_categories`.`usergroup_ids` = '') or (0 <> find_in_set(0,`cscartdb`.`cscart_categories`.`usergroup_ids`)) or (0 <> find_in_set(1,`cscartdb`.`cscart_categories`.`usergroup_ids`))) and (`cscartdb`.`cscart_categories`.`status` in ('A','H')))"
          }
        }
      ]
    }
  }
}