Updating Data with SQLSetPos


Applications can update or delete any row in the rowset with SQLSetPos. Calling SQLSetPos is a convenient alternative to constructing and executing an SQL statement. It lets an ODBC driver support positioned updates even when the data source does not support positioned SQL statements. It is part of the paradigm of achieving complete database access by means of function calls.

         SQLSetPos operates on the current rowset and can be used only after a call to SQLFetchScroll. The application specifies the number of the row to update, delete, or insert, and the driver retrieves the new data for that row from the rowset buffers. SQLSetPos can also be used to designate a specified row as the current row, or to refresh a particular row in the rowset from the data source.

Rowset size is set by a call to SQLSetStmtAttr with an Attribute argument of SQL_ATTR_ROW_ARRAY_SIZE. SQLSetPos uses a new rowset size, however, only after a call to SQLFetch or SQLFetchScroll. For example, if the rowset size is changed, SQLSetPos is called and then SQLFetch or SQLFetchScroll is called, and the call to SQLSetPos uses the old rowset size while SQLFetch or SQLFetchScroll uses the new rowset size.

The first row in the rowset is row number 1. The RowNumber argument in SQLSetPos must identify a row in the rowset; that is, its value must be in the range between 1 and the number of rows that were most recently fetched (which may be less than the rowset size). If RowNumber is 0, the operation applies to every row in the rowset.

Because most interaction with relational databases is done through SQL, SQLSetPos is not widely supported. However, a driver can easily emulate it by constructing and executing an UPDATE or DELETE statement.

To determine what operations SQLSetPos supports, an application calls SQLGetInfo with the SQL_DYNAMIC_CURSOR_ATTRIBUTES1, SQL_FORWARD_ONLY_CURSOR_ATTRIBUTES1, SQL_KEYSET_CURSOR_ATTRIBUTES1, or SQL_STATIC_CURSOR_ATTRIBUTES1 information option (depending on the type of the cursor).

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