Sandbox

SELECT 
  markers.* 
FROM 
  tmall_cp_advertisement_markers as markers 
WHERE 
  markers.object_id = 21 
  AND markers.object_type = 'category_banner' 
  AND markers.status = 'A'

Query time 0.00761

JSON explain

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