SELECT 
  shipping_id 
FROM 
  cscart_shippings 
WHERE 
  service_id = 714 
LIMIT 
  1

Query time 0.00020

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_shippings",
          "access_type": "ALL",
          "rows": 4,
          "filtered": 100,
          "attached_condition": "cscart_shippings.service_id = 714"
        }
      }
    ]
  }
}