Database and Artificial Intelligence (AI) can benefit from each other. On the one hand, AI can make database more intelligent (AI4DB) by exploiting learning-based techniques. On the other hand, database techniques can optimize AI models (DB4AI), such as reducing the complexity of using AI models and accelerating the deployment of AI algorithms. In this special section, we discuss 1) how to exploit AI or machine learning techniques for index design, performance tuning, query processing in database systems, and 2) how to utilize database and data management techniques to make AI models more reusable and more tolerant to dirty data.