MDAC 2.5 SDK - ODBC Programmer's Reference
Appendix F: ODBC Cursor Library

Executing Positioned Update and Delete Statements

After an application has fetched a block of data with SQLFetchScroll, it can update or delete the data in the block. To execute a positioned update or delete, the application:

1. Calls SQLSetPos to position the cursor on the row to be updated or deleted.
   
   
2. Constructs a positioned update or delete statement with the following syntax:

        UPDATE table-name
             SET column-identifier = {expression | NULL}
             [, column-identifier = {expression | NULL}]
             WHERE CURRENT OF cursor-name

        DELETE FROM table-name WHERE CURRENT OF cursor-name

   The easiest way to construct the SET clause in a positioned update statement is to use parameter markers for each column to be updated and use SQLBindParameter to bind these to the rowset buffers for the row to be updated. In this case, the C data type of the parameter will be the same as the C data type of the rowset buffer.

3. Updates the rowset buffers for the current row if it will execute a positioned update statement. After successfully executing a positioned update statement, the cursor library copies the values from each column in the current row to its cache.

   Caution   If the application does not correctly update the rowset buffers before executing a positioned update statement, the data in the cache will be incorrect after the statement is executed.

4. Executes the positioned update or delete statement using a different statement than the statement associated with the cursor.

Caution   The WHERE clause constructed by the cursor library to identify the current row can fail to identify any rows, identify a different row, or identify more than one row. For more information, see "Constructing Searched Statements," later in this appendix.

All positioned update and delete statements require a cursor name. To specify the cursor name, an application calls SQLSetCursorName before the cursor is opened. To use the cursor name generated by the driver, an application calls SQLGetCursorName after the cursor is opened.

After the cursor library executes a positioned update or delete statement, the status array, rowset buffers, and cache maintained by the cursor library contain the values shown in the following table.

[1]   The application must update the values in the rowset buffers before executing the positioned update statement; after executing the positioned update statement, the cursor library copies the values in the rowset buffers to its cache.