DB Projects Help >> Defining Cursors
In software, a collection cursor is a management design that allows traversal over the information in a collection. Cursors accomplish following management along with the traversal, such as collection, inclusion and eradication of collection information. The collection cursor feature of traversal creates cursors similar to the selection expressions strategy of iterator.
Cursors are used by collection developers to procedure person series come back by collection program issues. Cursors help treatment of whole effect pieces at once-ability that most step-by-step selection different languages shortage. In these circumstances, a cursor allows the series in a result-set to be refined sequentially.
In SQL processes, a cursor develop it possible to explain an effect set (a set of information rows) and accomplishes complicated sense on a row by row groundwork. By using the same aspects, an SQL method can also explain an effect set and come back it immediately to the call of the SQL method or to customer software.
A cursor can be considered as a suggestion to one row in a set of series. The cursor can only guide one row at once, but can go to other series of the effect set as wanted. To use cursors in SQL processes, you need to do the following:
Declare a cursor that defines a result set.
Open the cursor to establish the result set.
Fetch the data into local variables as needed from the cursor, one row at a time.
Close the cursor when done
To operate with cursors you must use the following SQL statements:
Developers may assert cursors as scrollable or not scrollable. The scroll ability indicates the route in which a cursor can go.
DECLARE cursor_name sensitivity SCROLL CURSOR FOR SELECT ... FROM...
With a non-scrollable cursor, also known as forward-only, one can FETCH each row at most once and the cursor instantly techniques to the instantly following row. A fetch function after the last row has been gathered jobs the cursor after the last row and dividends SQLSTATE 02000 (SQLCODE +100).
An application may location a scrollable cursor anywhere in the effect set using the FETCH SQL report. The key phrase SCROLL must be specified when proclaiming the cursor. The normal is NO SCROLL, although different expressions bindings like JDBC may submit an application different normal.
Cursors in distributed transactions
Using cursors in dispersed dealings (X/Open XA Environments), which are handled using a purchase check, is no different than cursors in non-distributed dealings.
One has to pay interest when using hold able cursors, however. Contacts can be used by different programs. Thus, once a purchase has been finished and dedicated, a following purchase (running in a different application) could end up with established hold able cursors. Therefore, a software creator has to be conscious of that scenario.
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