The Halloween problem is an update anomaly that can occur when a client using a cursor updates a column of the cursor result-set row, and that column defines the order in which the rows are returned from the table. For example, if a cursor was to use an index on last_name, first_name, and update one of these columns, the row could appear in the result set a second time.
To avoid the Halloween problem on data-only-locked tables, Adaptive Server chooses a table scan when the columns from an otherwise useful index are included in the column list of a for update clause.
For implicitly updatable cursors declared without a for update clause, and for cursors where the column list in the for update clause is empty, cursors that update a column in the index used by the cursor may encounter the Halloween problem.
