10. A relational database management system as recited in claim 7, wherein said optimizer exploits commonality among queries across multiple queries.
10. A relational database management system as recited in claim 7, wherein said optimizer exploits commonality among queries across multiple queries. 11. A relational database management system as recited in claim 10, wherein said relational database system further comprises a plan table which stories previously determined optimal plans for subqueries to exploit the commonality.