Question

Hoping someone can help me out with this.

Lets say I have a table called incoming_data with 4 columns:

primary_key_id serial_number counter selected_color 

I get data from a source that fills this table. The primary key has its identity turned on so it is not repeating. I will get duplicate serial numbers with different selected colors.

The counter is ever increasing coming from the device.

So what I want to do is select all the data I received today, group the data by serial number and only get the record with the highest counter value.

Simple:

SELECT      serial_number, MAX(counter) FROM        incoming_data  GROUP BY    serial number 

This works perfectly, except that I want to do something with the color information that I received.

If I add color to the select, then I get ALL the records since all the colors I received that day are different. That wont work.

If I could get the primary_key_id of the record then I could just query for the color but this doesn’t work either since each primary_key_id value is different I get them all.

Any suggestions on a better technique for doing this?

Thanks!

Answer 1

Extract the relevant key, then join back to get ‘non key’. This works in MS SQL Server and later Sybase.

SELECT      i.serial_number, i.counter, i.selected_color FROM    (    SELECT      serial_number, MAX(counter) AS maxc    FROM            incoming_data     GROUP BY    serial number    ) max    JOIN    incoming_data i ON max.serial_number = i.serial_number AND max.maxc = i.counter