Discovery and application of check constraints in DB2

The traditional role of integrity constraints is to protect the integrity of data, but integrity constraints can and do play other roles in databases; for example, they can be used for query optimization. In this role, they do not need to model the domain; it is sufficient that they describe regularities that are true about the data currently stored in a database. In this paper, we describe two algorithms for finding such regularities (in the syntactic form of check constraints) and discuss some of their applications in DB2. In particular, we show their use in query optimization.