Detection and prevention of writing conflicts within nested query statements

Conflict checking for writing operations in an SQL database system is carried 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 each nested statement is accessed and the information is compared with a list of tables maintained for the parent statement to determine if there is a read/write or write/write conflict possible if the nested statement is executed. Where there is no conflict detected, the information from the table access data structure is copied to the list of tables.