Some applications build SQL statements that cannot be completely specified in the application. In some cases, for example, statements depend on a response from the user before the application knows exactly what information to retrieve, such as when a reporting application allows a user to select which columns to display.
In such a case, the application needs a method for retrieving information about both the nature of the result set and the contents of the result set. The information about the nature of the result set, called a descriptor, identifies the data structure, including the number and type of columns expected to be returned. Once the application has determined the nature of the result set, retrieving the contents is straightforward.
This result set metadata (information about the nature and content of the data) is manipulated using descriptors. Obtaining and managing the result set metadata is called describing.
Since cursors generally produce result sets, descriptors and cursors are closely linked, although some interfaces hide the use of descriptors from the user. Typically, statements needing descriptors are either SELECT statements or stored procedures that return result sets.
A sequence for using a descriptor with a cursor-based operation is as follows:
For more information, see The SQL descriptor area (SQLDA).
Alternatively, you can use SQLDescribeCol and SQLColAttributes to obtain column information.
For more information about input and output parameters of the DESCRIBE statement, see DESCRIBE statement [ESQL].
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