Fixing operand data type varchar is invalid for sum operator
So, you're staring at your screen and that annoying operand data type varchar is invalid for sum operator message just popped up in SQL Server. It usually happens right when you think you've nailed a query, only to have the engine bark back at you because you're trying to do math on something it considers text. It's one of those "face-palm" moments for developers, but don't worry—it's actually a really common hurdle, especially when dealing with messy data or legacy databases. ...