SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '668726d441672c915965a067c24081c997017cc67fd25a7a074a1a58b21d8e57' 
  AND token = '7bfZ/ercI+dVvppeHSoJlDNC3v2Kqw0hXOTJyTKAtpA=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00027

JSON explain

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