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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '31ff78d43150870adafc8146407587461c64bc5eb91810532063472f4c8ff385' 
  AND token = 'Ot3XbQeLt1asJtcMrXvLSrw2zJFdstUxo6idto/2HyM=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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