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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = '849faa8e528948870372e84e8f00b2995fce21ab734cb3895afc41497fba5118' 
  AND token = '3uaMWeK3+gr8t8sLfKOWhGF8xDiE5mxdAqD1MMKCG4w=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00025

JSON explain

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