A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
Excel will automatically format dates depending upon the data type it is given in the result set of the SQL query. it appears that in this case the date is being delivered to Excel as text.
The easy thing to do is to make calculated columnsdo the work of converting the text into Excel Dates. If your date comes through formatted as text 09/20/2015 you can use the DATEVALUE worksheet function in a calculated field to turn the text into a date number that can be formatted as a date.