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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = '540f6ca54e1c39deb608709ddb7af0a046b55e94f024b7d688e955770a318ae2' 
  AND token = '7xzHq9ji+kmmq019w9BPTa31Bf0EApiMeY9mOVchn9s=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00024

JSON explain

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