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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = '8a71f8fdea3a494428e6ff4e53571120932ac1fd7dc23f1dbd53035a1879ba35' 
  AND token = '5klqwORqFL0/b+KaaD2JFvygWaYKF9dqwA4EJW86uxI=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00027

JSON explain

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