How to: Discard Changes Made to Queries (Visual Database Tools)
You can discard changes made to a query definition prior to saving them. Once they have been saved, they cannot be returned to a previous state.
Note
To undo a change you've made to values in the Results pane, press the ESC key before you move off of the record. If you move off of a record and receive a notice that the changes will not be committed to the database you can also press the ESC key to revert to the previous value.
To discard changes made to a query definition
With the query open in Query and View Designer, from the File menu, click Close.
In the Microsoft SQL Server Management Studio dialog box, click No.
The query definition will return to the state it was in at the last save.