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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b3279646f3e7b1719b3a06bb739c51974140f0bf17b6d683eb14f0d0732622b3' 
  AND token = '52iC1K8fJddS7qAx4mjx6yMiOLlnHagsxtja/WvIdag=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00021

JSON explain

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