DETECTION AND PREVENTION OF WRITING CONFLICTS WITHIN NESTED QUERY STATEMENTS

摘要

Conflict checking for writing operations in an SQL database system is carrie d out for nested statements invoked by a parent statement. Each statement has an associated table access data structure defined at compile-time indicating the tables in the database that the statement accesses and the mode of access. At execution-time the table access data structure for ea ch nested statement is accessed and the information is compared with a list of tables maintained fo r the parent statement to determine if there is a read/write or write/write conflict possible if th e nested statement is executed. Where there is no conflict detected, the information from the tabl e access data structure is copied to the list of tables.