SELECT 
  `shipping_id` 
FROM 
  cscart_shippings 
WHERE 
  wk_en_delivery_time = 'Y' 
  AND shipping_id = 6

Query time 0.00510

JSON explain

{
  "query_block": {
    "select_id": 1,
    "message": "Impossible WHERE noticed after reading const tables"
  }
}