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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '21e11e72f06f267f0780ba2730e141109c0549000e62d31414e456a405aa50e5' 
  AND token = '8HoSRtWSRTAmZeRzuOFPpuVQU81AqToY4+nLDMDNIs0=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00034

JSON explain

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