SELECT 
  *, 
  amount AS pure_amount 
FROM 
  cscart_reward_points 
WHERE 
  object_id = 50175 
  AND object_type = 'P' 
  AND company_id = 0 
  AND amount > 0 
  AND usergroup_id IN(0, 1) 
ORDER BY 
  amount_type ASC, 
  amount ASC 
LIMIT 
  1

Query time 0.00066

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "0.35"
    },
    "ordering_operation": {
      "using_filesort": true,
      "table": {
        "table_name": "cscart_reward_points",
        "access_type": "range",
        "possible_keys": [
          "unique_key"
        ],
        "key": "unique_key",
        "used_key_parts": [
          "object_id",
          "usergroup_id",
          "object_type",
          "company_id"
        ],
        "key_length": "13",
        "rows_examined_per_scan": 2,
        "rows_produced_per_join": 0,
        "filtered": "33.33",
        "index_condition": "((`s2cart`.`cscart_reward_points`.`company_id` = 0) and (`s2cart`.`cscart_reward_points`.`object_id` = 50175) and (`s2cart`.`cscart_reward_points`.`object_type` = 'P') and (`s2cart`.`cscart_reward_points`.`usergroup_id` in (0,1)))",
        "cost_info": {
          "read_cost": "0.25",
          "eval_cost": "0.02",
          "prefix_cost": "0.35",
          "data_read_per_join": "5"
        },
        "used_columns": [
          "reward_point_id",
          "object_id",
          "usergroup_id",
          "amount",
          "amount_type",
          "object_type",
          "company_id"
        ],
        "attached_condition": "(`s2cart`.`cscart_reward_points`.`amount` > 0)"
      }
    }
  }
}