Builds and returns a unique key query field.
Adds the unique key as a field (as a display column) in the query's search results. The display column is added to the list so its number, or column value (for GetColumnValue), is one higher than the last column added to the list (or 1 if it is the first column).
The IsShown property (of the returned QueryFieldDef object) must be set to True for the field to be added to the display list. If the value for the IsShown property is set to False, the unique key is not added to the query result set as a column.
A unique key is the same value as the display name for a record. For more information, see Record types