Open data are gold mines because they can be used to create services that develop a smart city while improving users' living conditions. Several research works go in this direction, presenting open data impact in the smart city for some, while others have focused on data processing methods. We have therefore deemed it necessary to make a state of the art on these different issues. The particularity of our study is that it shows the link between open data and smart city in all its aspects, describing what kind of open data is suitable for the smart city, how it is important for its development, and how these open data are processed to create services. Thus, in this article, we first present a review of existing surveys since 2015. Then, we present different smart city dimensions based on open data as well as some applications, and we detail how to process these data. We end with a list of open data sources as well as some challenges and solutions related to smart city services.