SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b2e5104bdcb36f535b00c5f2192575bc3f170fc0656859d2ce33b8bfede8305a' 
  AND token = '251Xo2KQBDVTiq4nQP7cZhyUMy2NuGizJabmDbiEtqk=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00031

JSON explain

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