SELECT 
  object_id, 
  thread_id, 
  type, 
  object_type 
FROM 
  cscart_discussion 
WHERE 
  1 
  AND object_id = 43434 
  AND object_type = 'P'

Query time 0.00040

JSON explain

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