SELECT 
  cscart_multi_decproducts_categories.product_id, 
  GROUP_CONCAT(
    IF(
      cscart_multi_decproducts_categories.link_type = "M", 
      CONCAT(
        cscart_multi_decproducts_categories.category_id, 
        "M"
      ), 
      cscart_multi_decproducts_categories.category_id
    )
  ) AS category_ids 
FROM 
  cscart_multi_decproducts_categories 
  INNER JOIN cscart_multi_deccategories ON cscart_multi_deccategories.category_id = cscart_multi_decproducts_categories.category_id 
  AND cscart_multi_deccategories.storefront_id IN (0, 1) 
  AND (
    cscart_multi_deccategories.usergroup_ids = '' 
    OR FIND_IN_SET(
      0, cscart_multi_deccategories.usergroup_ids
    ) 
    OR FIND_IN_SET(
      1, cscart_multi_deccategories.usergroup_ids
    )
  ) 
  AND cscart_multi_deccategories.status IN ('A', 'H') 
WHERE 
  cscart_multi_decproducts_categories.product_id IN (
    25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 
    36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 
    46, 47, 48
  ) 
GROUP BY 
  cscart_multi_decproducts_categories.product_id

Query time 0.00067

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "31.33"
    },
    "grouping_operation": {
      "using_temporary_table": true,
      "using_filesort": true,
      "cost_info": {
        "sort_cost": "0.70"
      },
      "nested_loop": [
        {
          "table": {
            "table_name": "cscart_multi_deccategories",
            "access_type": "ALL",
            "possible_keys": [
              "PRIMARY",
              "c_status",
              "p_category_id"
            ],
            "rows_examined_per_scan": 84,
            "rows_produced_per_join": 3,
            "filtered": "4.00",
            "cost_info": {
              "read_cost": "19.61",
              "eval_cost": "0.67",
              "prefix_cost": "20.28",
              "data_read_per_join": "8K"
            },
            "used_columns": [
              "category_id",
              "storefront_id",
              "usergroup_ids",
              "status"
            ],
            "attached_condition": "((`vishalecarter_multi_dec`.`cscart_multi_deccategories`.`storefront_id` in (0,1)) and ((`vishalecarter_multi_dec`.`cscart_multi_deccategories`.`usergroup_ids` = '') or find_in_set(0,`vishalecarter_multi_dec`.`cscart_multi_deccategories`.`usergroup_ids`) or find_in_set(1,`vishalecarter_multi_dec`.`cscart_multi_deccategories`.`usergroup_ids`)) and (`vishalecarter_multi_dec`.`cscart_multi_deccategories`.`status` in ('A','H')))"
          }
        },
        {
          "table": {
            "table_name": "cscart_multi_decproducts_categories",
            "access_type": "ref",
            "possible_keys": [
              "PRIMARY",
              "pt"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "category_id"
            ],
            "key_length": "3",
            "ref": [
              "vishalecarter_multi_dec.cscart_multi_deccategories.category_id"
            ],
            "rows_examined_per_scan": 2,
            "rows_produced_per_join": 0,
            "filtered": "10.45",
            "index_condition": "(`vishalecarter_multi_dec`.`cscart_multi_decproducts_categories`.`product_id` in (25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48))",
            "cost_info": {
              "read_cost": "9.00",
              "eval_cost": "0.14",
              "prefix_cost": "30.63",
              "data_read_per_join": "11"
            },
            "used_columns": [
              "product_id",
              "category_id",
              "link_type"
            ]
          }
        }
      ]
    }
  }
}