DAO QueryDefs

Ø A DAO querydef, represented in MFC by a CDaoQueryDefobject, is a query definition.

Ø The object defines the SQL statement for a query and provides operations for executing the query, for saving it in the database for reuse, for parameterizing the query, and more.

Ø Saved queries are advantageous because you can keep frequently used queries, especially complex ones, for easy reuse later.

Ø USES:

·        Creating recordsets, which you then open to run the query.

•Directly executing queries that don't return records. These include action queries and some SQL pass-through queries (those that return no records).

Ø QueryDef Parameters:A query parameter is an element containing a value that you can change to affect the results of the query. For example, a query returning data about an employee might have a parameter for the employee's name. It has two major advantages:

·        It can result in better execution speed, particularly on the second and subsequent requeries.

·        It lets you build a query at run time, based on information not available to you at design time, such as information that you must obtain from the user or information that you must calculate.

Ø Each DAO database object maintains a QueryDefs collection — a collection of all saved querydefs in the database. Each querydef object maintains two collections of its own:

·  Parameters.  All defined parameters for the query.

·  Fields.  The fields in one or more tables that correspond to the parameters. For example, an Employee Name field corresponds to an Employee Name parameter.