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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = '15a2436f373c6a6cb7b071a489cb90861bbf6988de8bac87e57ce73c1fb4a1c9' 
  AND token = '1v31wJW9Im9svxuydjEn8PSvU7UYYModZcT2ZqNvilg=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00035

JSON explain

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