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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '28e1629ed5f1b8c7dcc6f14cddbc55059895eeabcdb1fd048a7fd2a26ad0c876' 
  AND token = 'RmUmJgjnRSBQrjAFNZrn7YMOEQxJMlt+fEk1PMOruHc=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00055

JSON explain

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