SELECT 
  feature_id 
FROM 
  cscart_product_features 
WHERE 
  feature_id IN (712) 
  AND feature_type = 'E'

Query time 0.00023

JSON explain

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