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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = '793d91421ee9036653d3e16797306aed8851256a516c00339517395f7c30541f' 
  AND token = 'gAUazLQS4bWGTYG8fPHermVRcGL2tw2DDHDeUcq5rSE=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00021

JSON explain

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