SELECT 
  `lastname`, 
  `firstname` 
FROM 
  `cscart_users` 
WHERE 
  `company_id` = 302

Query time 0.00055

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "70.00"
    },
    "table": {
      "table_name": "cscart_users",
      "access_type": "ALL",
      "rows_examined_per_scan": 650,
      "rows_produced_per_join": 65,
      "filtered": "10.00",
      "cost_info": {
        "read_cost": "63.50",
        "eval_cost": "6.50",
        "prefix_cost": "70.00",
        "data_read_per_join": "701K"
      },
      "used_columns": [
        "company_id",
        "firstname",
        "lastname"
      ],
      "attached_condition": "(`dev2`.`cscart_users`.`company_id` = 302)"
    }
  }
}