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Transact-SQL User's Guide

Chapter 17 Cursors: Accessing Data Row by Row

Join cursor processing and data modifications

Recommendations

Recommendations

In general, applications should attempt to avoid updating join columns or columns with search clauses and other predicates to change their value when cursor scans are in progress.

• Avoid updates to the join columns of cursors or to the search arguments of join cursors whenever possible, unless you are completely sure of the join order.

• Use a cursor query that creates a worktable, and then use searched updates and deletes on the base table. When a cursor select query requires a worktable, the cursor is always insensitive to changes to the underlying table. Cursors that include order by, distinct, group by, or other clauses that create a worktable cannot be updated with positioned updates.

• If you are using cursors to update both join columns, consider using searched updates instead of positioned updates. Although further fetches may return buffered values instead of values that have been changed in the data rows, use of searched updates avoids the possibility of failing to fetch matching rows due to the choice of join order. Searched updates to a clustered index key in an allpages-locked table implicitly close the cursor.

• Note that the ANSI SQL 92 entry-level specification does not allow updates to join columns using cursors, so the behavior is implementation-specific. Applications designed to be portable across different database software must take individual implementations into account.