Institute of Electrical & Electronic Engineers
Persistent data of most business applications contain recursive data structures, i.e. hierarchies and networks. Processing such data stored in relational databases is not straight-forward, since the relational algebra and calculus do not provide adequate facilities. Therefore, it is not surprising that initial SQL standards do not contain recursion as well. Although it was introduced by SQL: 1999, even now it is implemented in few selected database management systems. In particular, one of the most popular DBMSs (MySQL) does support recursive queries yet.