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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = '138704569db3c67e6f8c344962062d9d150fd518c339fe18d5c08700761997f3' 
  AND token = '7FV402fC4fSUaXScwJDbZe7+LZ4lUVIRjj+eQTr+NoI=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00033

JSON explain

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