Why do I need to explicitly specify all columns in a SQL “GROUP BY” clause - why not “GROUP BY *”?

Question

This has always bothered me - why does the GROUP BY clause in a SQL statement require that I include all non-aggregate columns? These columns should be included by default -

Answer 1

It's simple just like this: you asked to sql group the results by every single column in the from clause, meaning for every column in the from clause SQL, the sql engine will internally group the result sets before to present it to you. So that explains why it ask you to mention all the columns present in the from too because its not possible group it partially. If you mentioned the group by clause that is only possible to sql achieve your intent by grouping all the columns as well. It's a math restriction.