Method, system and program for simplifying data flow in a statement with sequenced subexpressions

摘要

Data flow in a database statement for a database management system having memory storing a database is simplified. The statement has at least two sequenced subexpressions, evaluation of which is driven by a sequencing operation. A reference to a first sequenced subexpression in a second sequenced subexpression subsequent to the first sequenced subexpression is determined. The reference affirming evaluation of the first sequenced subexpression is determined. A first evaluation order for conflicting table accesses between the first sequenced subexpression and other table accesses in the statement is determined. A second evaluation order between the other table accesses and the determined reference is also determined. The sequencing operation for the first sequenced subexpression is modified based on a sequential arrangement of the determined reference and the first sequenced subexpression according to the first evaluation order and the second evaluation order.