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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '51f092f08c581cef2850b068892945a441d6c66b914d76f8b4e037d8c6f54a2d' 
  AND token = '6gJcExtWU2jMAvGNjFY0JLaBRe0/o9iPX/5cZnUQaFM=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00036

JSON explain

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