You can open a select, crosstab, or action query in Design view. You can also open a select or crosstab query in Datasheet view, to view the query's results.
You can't open an action query in Datasheet view to view its results. However, in Datasheet view you can preview the data that will be affected when you run the action query.
What do you want to do?
View the results of a select or crosstab query in Datasheet view
Switch between views of a query
Run a make-table, append, delete, or update query