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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b51ef65673827bf9919699f61faf631b66f815bfb7fe43a41778451c8404e888' 
  AND token = 'RF4JMVoMByrsyCGTAijk/TNzBXAsjcTYyLoWGzrhMoE=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00039

JSON explain

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