Similarity search and related issues are current topic in databases. Over the last ten years more then 6500 papers dealing with similarity in databases were published according to Web of Science. The rising in the number of articles in the recent years shows that the research in this direction is still in its early stage. From the wide range of topics related with similarities in databases, one received a considerable attention already, namely functional dependencies which take similarities into account. Our main concern in this paper is to review and critically examine the existing work on this topic. (C) 2016 Elsevier B.V. All rights reserved.