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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = 'ad2908afbd7e1cedca36dc5433da293498b5d4b79119a12b2729b47e9010a442' 
  AND token = 'UmXobYiDf4zQ48NQPslKBHVIJx9v2vpivgt4aiM+C60=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00035

JSON explain

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