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 (
    300, 303, 304, 305, 306, 307, 308, 309, 
    310, 311, 312, 313, 314, 315, 316
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00080

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "34.06"
    },
    "grouping_operation": {
      "using_temporary_table": true,
      "using_filesort": true,
      "cost_info": {
        "sort_cost": "0.49"
      },
      "nested_loop": [
        {
          "table": {
            "table_name": "cscart_categories",
            "access_type": "ALL",
            "possible_keys": [
              "PRIMARY",
              "c_status",
              "p_category_id"
            ],
            "rows_examined_per_scan": 86,
            "rows_produced_per_join": 3,
            "filtered": "4.00",
            "cost_info": {
              "read_cost": "19.95",
              "eval_cost": "0.69",
              "prefix_cost": "20.64",
              "data_read_per_join": "8K"
            },
            "used_columns": [
              "category_id",
              "storefront_id",
              "usergroup_ids",
              "status"
            ],
            "attached_condition": "((`atulecarter_atul_demo1`.`cscart_categories`.`storefront_id` in (0,1)) and ((`atulecarter_atul_demo1`.`cscart_categories`.`usergroup_ids` = '') or find_in_set(0,`atulecarter_atul_demo1`.`cscart_categories`.`usergroup_ids`) or find_in_set(1,`atulecarter_atul_demo1`.`cscart_categories`.`usergroup_ids`)) and (`atulecarter_atul_demo1`.`cscart_categories`.`status` in ('A','H')))"
          }
        },
        {
          "table": {
            "table_name": "cscart_products_categories",
            "access_type": "ref",
            "possible_keys": [
              "PRIMARY",
              "pt"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "category_id"
            ],
            "key_length": "3",
            "ref": [
              "atulecarter_atul_demo1.cscart_categories.category_id"
            ],
            "rows_examined_per_scan": 3,
            "rows_produced_per_join": 0,
            "filtered": "4.75",
            "index_condition": "(`atulecarter_atul_demo1`.`cscart_products_categories`.`product_id` in (300,303,304,305,306,307,308,309,310,311,312,313,314,315,316))",
            "cost_info": {
              "read_cost": "10.87",
              "eval_cost": "0.10",
              "prefix_cost": "33.57",
              "data_read_per_join": "7"
            },
            "used_columns": [
              "product_id",
              "category_id",
              "link_type"
            ]
          }
        }
      ]
    }
  }
}