Question

let’s say my table schema is like bellow (it’s only a simplified example):

MyTable (table name)
ID - int (unique, auto increment)
Message - string
Timestamp - Datetime

I want to select the number of ID, group them by message and order them by timestamp, so I’ll do something like this:

SELECT count (ID), Message FROM MyTable
GROUP BY (Message)
ORDER BY Timestamp desc

However, SQL Server management studio throws me this error:

Column 'Timestamp ' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause.

The problem is that if I put Timestamp in the Group By statement with Message, it messes up my grouping. The other suggestion to put Timestamp in an aggregate function doesn’t make sense (ordering by say, count(Timestamp) doesn’t mean anything…)

Any idea on how to do this?

Thanks a lot!

Answer 1

Let’s say the same message is in your table multiple times:

       1|the mackerel likes frying|1/1/1917
       2|at night all cats are grey|12/15/1956
       3|the mackerel likes frying|2/2/1918

And you want to group by the message-string, counting the number of times the message appears in the table:

      the mackerel likes frying|2
      at night all cats are grey|1

The timestamp column is NOT part of the aggregation aka the grouping, but is part of the detail row. It CANNOT appear in the grouping, because timestamp is not “it” (singular) but timestamps, they, plural. There are two different timestamps in the example above for the mackerel message. Which one would you choose? How would the query know which one it was? All you have at your disposal are the aggregate functions:

        min(timestamp)
        max(timestamp)
        count(timestamp)

and if it were other than a datetime, you’d also have AVG(timestamp).