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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = '4cfa81425916abe38da3816456d32ecafc4d9cdd843ca11f53dddd3a4f7c13a3' 
  AND token = 'X/fEBOlFh0pMLOiDG3Ie0hM2PrRPU1RDfWTVfKPUWYg=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00020

JSON explain

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