If you have an aggregation function (sum, avg, count) in your select clause or if you have a group by clause, all of your columns must be aggregated or grouped.<BR><BR>In the version of SQL that I ...

I realized how much easier my life would be if SQL had a mode() aggregate function. (I'm using it in the mathematical sense). I'm guessing that either I use SQL in a wierd way or there is a good ...

SQL window functions provide extremely powerful and useful features that let you work with observations more easily. Different types explained here.