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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = '9ddfa28f475d760804e6b638e9ea6d471dcfce5c54a8f28c9536ec800feae641' 
  AND token = '53tAo2oZQFEswefvWsjFxokDLg4iKqlMRetd2HJEmAk=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00025

JSON explain

{
  "query_block": {
    "select_id": 1,
    "message": "no matching row in const table"
  }
}