SELECT 
  COUNT(*) 
FROM 
  cscart_orders 
WHERE 
  user_id = 80 
  AND status = 'C' 
  AND is_parent_order = 'N'

Query time 0.00108

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_orders",
      "access_type": "index_merge",
      "possible_keys": ["user_id", "status"],
      "key_length": "3,3",
      "index_merge": {
        "intersect": {
          "range": {
            "key": "user_id",
            "used_key_parts": ["user_id"]
          },
          "range": {
            "key": "status",
            "used_key_parts": ["status"]
          }
        }
      },
      "rows": 1,
      "filtered": 100,
      "attached_condition": "cscart_orders.user_id = 80 and cscart_orders.`status` = 'C' and cscart_orders.is_parent_order = 'N'"
    }
  }
}