Sybase 12.4.2 manual Cursors and versioning, Cursor sensitivity, Cursor scrolling, 312

Cursors in transactions

The rows in a cursor, like those in a table, have no order associated with them. The FETCH command steps through the rows, but the order may appear random and can even be inconsistent. For this reason, you will want to impose an order by appending an ORDER BY phrase to your SELECT statement.

Cursors and versioning

When you use cursors, Adaptive Server IQ needs to be able to manage multiple versions within a single transaction. For example, assume that you open a cursor called cust_cursor at time x that uses the customer table. You then update that table later on at time y. Adaptive Server IQ needs to retain the version of the customer table from time x until you are done using cust_cursor.

See “Effect of rollback” for what happens to cursors during a rollback of the database.

Adaptive Server IQ's support for cursors is oriented toward their likely use in DSS applications. The following sections discuss specific cursor characteristics with implications for transaction processing.

Cursor sensitivity

A cursor is said to be sensitive if its membership—the data rows it returns— can vary from the time it is opened until the time it is closed. An insensitive cursor has its membership fixed when it is opened. Adaptive Server IQ supports only insensitive cursors.

Cursor scrolling

Adaptive Server IQ cursors can be either scrolling or non-scrolling. Non- scrolling cursors allow only the command forms FETCH NEXT and FETCH RELATIVE 0 to find and retrieve data. They do not keep track of which rows have been fetched. A cursor declared as DYNAMIC SCROLL is the same as a cursor declared as SCROLL.

You can force all cursors to be non-scrolling by setting the option

FORCE_NO_SCROLL_CURSORS to ON. You may want to use this option to save on temporary storage requirements if you are retrieving very large numbers (millions) of rows.

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