On estimating the cardinality of the projection of a database relation
Rafiul Ahad, K. V. Bapa, Dennis J. McLeod · ACM Transactions on Database Systems · 1989
We present an analytical formula for estimating the cardinality of the projection on certain attributes of a subset of a relation in a relational database. This formula takes into account a priori knowledge of the semantics of the real-world objects and relationships that the database is intended to represent. Experimental testing of the formula shows that it has an acceptably low percentage error, and that its worst-case error is smaller than the best-known formula. Furthermore, the formula presented here has the advantage that it does not require a scan of the relation.