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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = '55b6948e0ce5c2201c3fdae5bb3b080681d9d410a283768046a995e65a0e45dc' 
  AND token = '9FQTlVTH4ACVj9oE0kVDXWOWfKgZ9ez+TTwcXAAe1Sc=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00035

JSON explain

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