SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '91e50ca0e3f0bff4454acb87f85d12d2fe8280e982cd33292dbca7067aa474a7' 
  AND token = '6KmEFjiZ+edG8lZd1VDcb3Rz4iigQu2XcYIKiSdFmyk=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00030

JSON explain

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