System and method for mutation of selected assignment operations on large data objects

摘要

A relational data base management system that stores and retrieves large data objects (LOBs) from data base storage to evaluate assignment statements includes a data manager that mutates selected string operations into equivalent functions on a LOB operand that can be left in the data base, thereby eliminating the associated storage access operations. When the data manager receives an assignment statement containing one or more LOBs, the data manager first checks to determine if the statement can be mutated. If the statement can be mutated, then the mutation is performed. The mutated statement is then processed according to a conventional deleted evaluation scheme. If the assignment statement cannot be mutated, then the statement is evaluated according to a conventional deleted evaluation scheme. In this way, the data base management system does not require the LOB to be read from the data base into intermediate storage, but instead provides an equivalent result by operating on the LOB in place in the data base storage. This permits processing selected LOB assignment statements with much fewer storage access operations than an immediate evaluation scheme, thereby increasing efficiency and execution speed.