How does DESelect handle errors in SQL queries?

deselect has a lot of functionality to try to prevent errors from happening in the first place for example, on the target definition screen, deselect provide all kind of warnings in the mapping section to make sure the user creates a mapping the minimizes the chance of errors deselect will warn when a user maps fields of different field types the target data extension field's length is shorter a required field is not mapped or mapped with a field that may contain null values despite the above, there are still errors that could occur during runtime that can not be detected beforehand if such error occurs the user will be notified if an error occurs during preview error is shown on the preview screen if an error occurs during run status icon of the selection on the home page will be a red warning icon click on the red warning icon to see the details of the error deselect will also provide as much useful information to the user as possible, typically more than what marketing cloud would return if an error occurs, the whole transaction will be reverted and no results will be written to the target data extension