There's more than one reason why you may receive this error, but the most common reason is that your order by statement column list doesn't correlate with your intended column-to-retrieve list when you happen to be using DISTINCT. This is usually easy to spot. A more obscure reason may be that you are using a function around one of the selected columns --but omitting to use the same function around the same selected column name in the order by statement. Here's an example: select distinct upper(columnA) ......