Abstract: A system and method of determining uniqueness properties of an expression. A root of the expression is first determined, where the root is one of a base relation, a unary operation or a binary operation. Once the root is determined, a first procedure of an augmented unique process is called to determine uniqueness properties of a child of that root. The procedure called is chosen based on the determined root. Where the root is a base relation, a first procedure of a uniqueness process is applied to determine the uniqueness properties of the base relation. Where the root is a unary or binary operation, the called procedure is suspended, a second procedure of the augmented unique process is called to determine the uniqueness properties of the child of the operation, and this process is repeated until a base relation is reached. Once a base relation is reached, the first procedure of the uniqueness process is applied to determine the uniqueness properties of the reached base relation.

Abstract: The present invention discloses a method and apparatus for the enumeration of projections (i.e., "SELECT DISTINCT" operations) in SQL queries containing outer and full outer joins in the presence of inner joins without encountering any regression in performance. The present invention removes projections from a given user query by moving the projections to the top of an expression tree representation of the query, wherein the projection removal is performed using algebraic identities rather than rule-based transformations. The present invention also discloses several methods of enumerating different plans or schedules for projection operations and binary operations in the given user query. The present invention can significantly reduce the execution time of a query by selecting the optimal schedule for binary operations and projections between the binary operations.

Abstract: A method and apparatus for reordering complex SQL queries containing joins, outer and full outer joins. The method and apparatus first translates the query into a hypergraph representation. Required sets, conflict sets and preserved sets are then generated for the query hypergraph. Using the required sets, a plurality of plans are enumerated, wherein the plans represent associative reorderings of relations in the query. SQL operators are selectively assigned to each of the enumerated plans using the conflict sets and/or preserved sets, so that the results from the plans are identical to the original query. A novel Modified General Outer Join (MGOJ) operator may be assigned to the root of a sub-tree, wherein the MGOJ operator is a compensation operator. The operator assignment is performed recursively for the root of each sub-tree in the plan. One of the enumerated plans (generally the most optimal) is then selected for execution.

Abstract: A system and method of determining uniqueness properties of an expression. A root of the expression is first determined, where the root is one of a base relation, a unary operation or a binary operation. Once the root is determined, a first procedure of an augmented unique process is called to determine uniqueness properties of a child of that root. The procedure called is chosen based on the determined root. Where the root is a base relation, a first procedure of a uniqueness process is applied to determine the uniqueness properties of the base relation. Where the root is a unary or binary operation, the called procedure is suspended, a second procedure of the augmented unique process is called to determine the uniqueness properties of the child of the operation, and this process is repeated until a base relation is reached. Once a base relation is reached, the first procedure of the uniqueness process is applied to determine the uniqueness properties of the reached base relation.