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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = '520ed78d490a3a376eed6657aae2aa843690aabc36fad94073286975bc5ce919' 
  AND token = 'DwyJgWcfMgTKOKt1y4jGMauJgP+2N3jVCt7usS1Plso=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00021

JSON explain

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